Network Working Group A. Phillips, Ed.
Internet-Draft Quest Software
Expires: September 11, 2005 M. Davis, Ed.
IBM
March 10, 2005
Tags for Identifying Languages
draft-ietf-ltru-registry-00
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Copyright (C) The Internet Society (2005).
Abstract
This document describes the structure, content, construction, and
semantics of language tags for use in cases where it is desirable to
indicate the language used in an information object. It also
describes how to register values for use in language tags and the
creation of user defined extensions for private interchange. This
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document obsoletes RFC 3066 (which replaced RFC 1766).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Language Tag . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Length Considerations . . . . . . . . . . . . . . . . 5
2.2 Language Subtag Sources and Interpretation . . . . . . . . 6
2.2.1 Primary Language Subtag . . . . . . . . . . . . . . . 7
2.2.2 Extended Language Subtags . . . . . . . . . . . . . . 9
2.2.3 Script Subtag . . . . . . . . . . . . . . . . . . . . 9
2.2.4 Region Subtag . . . . . . . . . . . . . . . . . . . . 10
2.2.5 Variant Subtags . . . . . . . . . . . . . . . . . . . 11
2.2.6 Extension Subtags . . . . . . . . . . . . . . . . . . 11
2.2.7 Private Use Subtags . . . . . . . . . . . . . . . . . 12
2.2.8 Pre-Existing RFC 3066 Registrations . . . . . . . . . 13
2.2.9 Possibilities for Registration . . . . . . . . . . . . 13
2.2.10 Classes of Conformance . . . . . . . . . . . . . . . 14
2.3 Choice of Language Tag . . . . . . . . . . . . . . . . . . 15
2.4 Meaning of the Language Tag . . . . . . . . . . . . . . . 16
2.4.1 Canonicalization of Language Tags . . . . . . . . . . 17
2.5 Considerations for Private Use Subtags . . . . . . . . . . 18
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . 20
3.1 Format of the IANA Language Subtag Registry . . . . . . . 20
3.2 Stability of IANA Registry Entries . . . . . . . . . . . . 24
3.3 Registration Procedure for Subtags . . . . . . . . . . . . 27
3.4 Extensions and Extensions Namespace . . . . . . . . . . . 30
4. Security Considerations . . . . . . . . . . . . . . . . . . 32
5. Character Set Considerations . . . . . . . . . . . . . . . . 33
6. Changes from RFC 3066 . . . . . . . . . . . . . . . . . . . 34
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 38
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 39
B. Examples of Language Tags (Informative) . . . . . . . . . . 40
C. Conversion of the RFC 3066 Language Tag Registry . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . . 44
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1. Introduction
Human beings on our planet have, past and present, used a number of
languages. There are many reasons why one would want to identify the
language used when presenting or requesting information.
Information about a user's language preferences commonly needs to be
identified so that appropriate processing can be applied. For
example, the user's language preferences in a browser can be used to
select web pages appropriately. A choice of language preference can
also be used to select among tools (such as dictionaries) to assist
in the processing or understanding of content in different languages.
In addition, knowledge about the particular language used by some
piece of information content may be useful or even required by some
types of information processing; for example spell-checking,
computer-synthesized speech, Braille transcription, or high-quality
print renderings.
One means of indicating the language used is by labeling the
information content with a language identifier. These identifiers
can also be used to specify user preferences when selecting
information content, or for labeling additional attributes of content
and associated resources.
These identifiers can also be used to indicate additional attributes
of content that are closely related to the language. In particular,
it is often necessary to indicate specific information about the
dialect, writing system, or orthography used in a document or
resource, as these attributes may be important for the user to obtain
information in a form that they can understand, or important in
selecting appropriate processing resources for the given content.
This document specifies an identifier mechanism and a registration
function for values to be used with that identifier mechanism. It
also defines a mechanism for private use values and future extension.
This document replaces RFC 3066, which replaced RFC 1766. For a list
of changes in this document, see Section 6.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119] [11].
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2. The Language Tag
2.1 Syntax
The language tag is composed of one or more parts: A primary language
subtag and a (possibly empty) series of subsequent subtags. Subtags
are distinguished by their length, position in the subtag sequence,
and content, so that each type of subtag can be recognized solely by
these features. This makes it possible to construct a parser that
can extract and assign some semantic information to the subtags, even
if specific subtag values are not recognized. Thus a parser need not
have an up-to-date copy of the registered subtag values to perform
most searching and matching operations.
The syntax of this tag in ABNF [RFC 2234] [13] is:
Language-Tag = (lang
*("-" extlang)
["-" script]
["-" region]
*("-" variant)
*("-" extension)
["-" privateuse])
/ privateuse ; private-use tag
/ grandfathered ; grandfathered registrations
lang = 2*3ALPHA ; shortest ISO 639 code
/ registered-lang
extlang = 3ALPHA ; reserved for future use
script = 4ALPHA ; ISO 15924 code
region = 2ALPHA ; ISO 3166 code
/ 3DIGIT ; UN country number
variant = ALPHA (4*7alphanum) ; registered variants
/ DIGIT (3*7alphanum)
extension = singleton 1*("-" (2*8alphanum)) ; extension subtag(s)
privateuse = ("x"/"X") 1*("-" (1*8alphanum)) ; private use subtag(s)
singleton = ("a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z")
; Single letters: x/X is reserved for private use
registered-lang = 4*8ALPHA ; registered language subtag
grandfathered = 1*3ALPHA 1*2("-" (2*8alphanum)) ; grandfathered registration
; Note: i is the only singleton that starts
; a grandfathered tag
alphanum = (ALPHA / DIGIT) ; letters and numbers
Figure 1: Language Tag ABNF
The character "-" is HYPHEN-MINUS (ABNF: %x2D). Note that there is a
subtlety in the ABNF for 'variant': variants may consist of sequences
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of up to eight characters.
Whitespace is not permitted in a language tag. For examples of
language tags, see Appendix B.
Note that although [RFC 2234] [13] refers to octets, the language
tags described in this document are sequences of characters from the
US-ASCII repertoire. Language tags may be used in documents and
applications that use other encodings, so long as these encompass the
US-ASCII repertoire. An example of this would be an XML document
that uses the Unicode UTF-16LE encoding.
The tags and their subtags, including private-use and extensions, are
to be treated as case insensitive: there exist conventions for the
capitalization of some of the subtags, but these should not be taken
to carry meaning.
For example:
o [ISO 639] [1] recommends that language codes be written in lower
case ('mn' Mongolian).
o [ISO 3166] [4] recommends that country codes be capitalized ('MN'
Mongolia).
o [ISO 15924] [3] recommends that script codes use lower case with
the initial letter capitalized ('Cyrl' Cyrillic).
However, in the tags defined by this document, the uppercase US-ASCII
letters in the range 'A' (ABNF: %x41) through 'Z' (ABNF: %x5A) are
considered equivalent and mapped directly to their US-ASCII lowercase
equivalents in the range 'a' (ABNF: %x61) through 'z' (ABNF: %x7A).
Thus the tag "mn-Cyrl-MN" is not distinct from "MN-cYRL-mn" or
"mN-cYrL-Mn" (or any other combination) and each of these variations
conveys the same meaning: Mongolian written in the Cyrillic script as
used in Mongolia.
For informative examples of language tags, see Appendix B at the end
of this document.
2.1.1 Length Considerations
Although neither the ABNF nor other guidelines in this document
provide a fixed upper limit on the number of size of subtags in a
Language Tag and it is possible to envision quite long and complex
subtag sequences, in practice these are rare because additional
granularity in tags seldom adds useful distinguishing information and
because longer, more granular tags interefere with the meaning,
understanding, and processing of language tags.
In particular, variant subtags SHOULD be used only with their
recommended prefix. This limits most tags to a sequence of four
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subtags (excluding any extensions or private use sequences). See
Section 2.3 for more information on selecting the most appropriate
Language Tag.
A conformant implementation need not support the storage of language
tags which exceed a specified length. For an example, see [RFC 2231]
[12]. Any such a limitation MUST be clearly documented, and such
documentation SHOULD include the disposition of any longer tags (for
example, whether an error value is generated or the language tag is
truncated). If truncation is permitted it SHOULD NOT permit a subtag
to be divided.
2.2 Language Subtag Sources and Interpretation
The namespace of language tags and their subtags is administered by
the Internet Assigned Numbers Authority (IANA) [17] according to the
rules in Section 3 of this document. The registry maintained by IANA
is the source for valid subtags: other standards referenced in this
section provide the source material for that registry.
Terminology in this section:
o Tag or tags refers to a complete language tag, such as
"fr-Latn-CA". Examples of tags in this document are enclosed in
double-quotes ("en-US").
o Subtag refers to a specific section of a tag, separated by hyphen,
such as the subtag 'Latn' in "fr-Latn-CA". Examples of subtags in
this document are enclosed in single quotes ('Latn').
o Code or codes refers to tags defined in external standards (and
which are used as subtags in this document). For example, 'Latn'
is an [ISO 15924] [3] script code which was used to define the
'Latn' script subtag for use in a language tag. Examples of codes
in this document are enclosed in single quotes ('en', 'Latn').
The definitions in this section apply to the various subtags within
the language tags defined by this document, excepting those
"grandfathered" tags defined in Section 2.2.8.
Language tags are designed so that each subtag has unique length and
content restrictions. These make identification of the subtag's type
possible, even if the content of the subtag itself is unrecognized.
This allows tags to be parsed and processed without reference to the
latest version of the underlying standards or the IANA registry and
makes the associated exception handling when parsing tags simpler.
Subtags in the IANA registry that do not come from an underlying
standard can only appear in specific positions in a tag.
Specifically, they can only occur as primary language subtags or as
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variant subtags.
Note that sequences of private-use and extension subtags MUST occur
at the end of the sequence of subtags and MUST NOT be interspersed
with subtags defined elsewhere in this document.
Single letter and digit subtags are reserved for current or future
use. These include the following current uses:
o The single letter subtag 'x' is reserved to introduce a sequence
of private-use subtags. The interpretation of any private-use
subtags is defined solely by private agreement and is not defined
by the rules in this section or in any standard or registry
defined in this document.
o All other single letter subtags are reserved to introduce
standardized extension subtag sequences as described in
Section 3.4.
The single letter subtag 'i' is used by some grandfathered tags, such
as "i-enochian", where it always appears in the first position and
cannot be confused with an extension.
2.2.1 Primary Language Subtag
The primary subtag is the first subtag in a language tag and cannot
be empty. Except as noted, the primary subtag is the language
subtag. The following rules apply to the assignment and
interpretation of the primary subtag:
o All 2-character language subtags were defined in the IANA registry
according to the assignments found in the standard ISO 639 Part 1,
"ISO 639-1:2002, Codes for the representation of names of
languages -- Part 1: Alpha-2 code" [ISO 639-1] [1], or using
assignments subsequently made by the ISO 639 Part 1 maintenance
agency or governing standardization bodies.
o All 3-character language subtags were defined in the IANA registry
according to the assignments found in ISO 639 Part 2, "ISO
639-2:1998 - Codes for the representation of names of languages --
Part 2: Alpha-3 code - edition 1" [ISO 639-2] [2], or assignments
subsequently made by the ISO 639 Part 2 maintenance agency or
governing standardization bodies.
o The subtags in the range 'qaa' through 'qtz' are reserved for
private use in language tags. These subtags correspond to codes
reserved by ISO 639-2 for private use. These codes MAY be used
for non-registered primary-language subtags (instead of using
private-use subtags following 'x-'). Please refer to Section 2.5
for more information on private use subtags.
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o All language subtags of 4 to 8 characters in length in the IANA
registry were defined via the registration process in Section 3.3
and MAY be used to form the primary language subtag. At the time
this document was created, there were no examples of this kind of
subtag and future registrations of this type will be discouraged:
primary languages are STRONGLY RECOMMENDED for registration with
ISO 639 and subtags rejected by ISO 639 will be closely
scrutinized before they are registered with IANA.
o The single character subtag 'x' as the primary subtag indicates
that the language tag consists solely of subtags whose meaning is
defined by private agreement. For example, in the tag "x-fr-CH",
the subtags 'fr' and 'CH' should not be taken to represent the
French language or the country of Switzerland (or any other value
in the IANA registry) unless there is a private agreement in place
to do so. See Section 2.5.
o Other values MUST NOT be assigned to the primary subtag except by
revision or update of this document.
Note: For languages that have both an ISO 639-1 2-character code and
an ISO 639-2 3-character code, only the ISO 639-1 2-character code is
defined in the IANA registry.
Note: For languages that have no ISO 639-1 2-character code and for
which the ISO 639-2/T (Terminology) code and the ISO 639-2/B
(Bibliographic) codes differ, only the Terminology code is defined in
the IANA registry. At the time this document was created, all
languages that had both kinds of 3-character code were also assigned
a 2-character code; it is not expected that future assignments of
this nature will occur.
Note: To avoid problems with versioning and subtag choice as
experienced during the transition between RFC 1766 and RFC 3066, as
well as the canonical nature of subtags defined by this document, the
ISO 639 Registration Authority Joint Advisory Committee (ISO
639/RA-JAC) has included the following statement in [6]:
"A language code already in ISO 639-2 at the point of freezing ISO
639-1 shall not later be added to ISO 639-1. This is to ensure
consistency in usage over time, since users are directed in Internet
applications to employ the alpha-3 code when an alpha-2 code for that
language is not available."
In order to avoid instability of the canonical form of tags, if a
2-character code is added to ISO 639-1 for a language for which a
3-character code was already included in ISO 639-2, the 2-character
code will not be added as a subtag in the registry. See Section 3.2.
For example, if some content were tagged with 'haw' (Hawaiian), which
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currently has no 2-character code, the tag would not be invalidated
if ISO 639-1 were to assign a 2-character code to the Hawaiian
language at a later date.
For example, one of the grandfathered IANA registrations is
"i-enochian". The subtag 'enochian' could be registered in the IANA
registry as a primary language subtag (assuming that ISO 639 does not
register this language first), making tags such as "enochian-AQ" and
"enochian-Latn" valid.
2.2.2 Extended Language Subtags
The following rules apply to the extended language subtags:
o Three letter subtags immediately following the primary subtag are
reserved for future standardization, anticipating work that is
currently under way on ISO 639.
o Extended language subtags MUST follow the primary subtag and
precede any other subtags.
o There MAY be any additional number of extended language subtags.
o Extended language subtags will not be registered except by
revision of this document.
o Extended language subtags MUST NOT be used to form language tags
except by revision of this document.
Example: In a future revision or update of this document, the tag
"zh-gan" (registered under RFC 3066) might become a valid
non-grandfathered tag in which the subtag 'gan' might represent the
Chinese dialect 'Gan'.
2.2.3 Script Subtag
The following rules apply to the script subtags:
o All 4-character subtags were defined according to ISO 15924
[3]--"Codes for the representation of the names of scripts":
alpha-4 script codes, or subsequently assigned by the ISO 15924
maintenance agency or governing standardization bodies, denoting
the script or writing system used in conjunction with this
language.
o Script subtags MUST immediately follow the primary language subtag
and all extended language subtags and MUST occur before any other
type of subtag described below.
o The subtags 'Qaaa' through 'Qabx' are reserved for private use in
language tags. These subtags correspond to codes reserved by ISO
15924 for private use. These codes MAY be used for non-registered
script values. Please refer to Section 2.5 for more information
on private-use subtags.
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o Script subtags cannot be registered using the process in
Section 3.3 of this document. Variant subtags may be considered
for registration for that purpose.
Example: "de-Latn" represents German written using the Latin script.
2.2.4 Region Subtag
The following rules apply to the region subtags:
o The region subtag defines language variations used in a specific
region, geographic, or political area. Region subtags MUST follow
any language, extended language, or script subtags and MUST
precede all other subtags.
o All 2-character subtags following the primary subtag were defined
in the IANA registry according to the assignments found in ISO
3166 [4]--"Codes for the representation of names of countries and
their subdivisions - Part 1: Country codes"--alpha-2 country codes
or assignments subsequently made by the ISO 3166 maintenance
agency or governing standardization bodies.
o All 3-character codes consisting of digit (numeric) characters
were defined in the IANA registry according to the assignments
found in UN Standard Country or Area Codes for Statistical Use
[5] or assignments subsequently made by the governing standards
body. Note that not all of the UN M.49 codes are defined in the
IANA registry:
* UN numeric codes assigned to 'macro-geographical (continental)'
or sub-regions not associated with an assigned ISO 3166 alpha-2
code _are_ defined.
* UN numeric codes for 'economic groupings' or 'other groupings'
are _not_ defined in the IANA registry and MUST NOT be used to
form language tags.
* Countries with ambiguous ISO 3166 alpha-2 codes as defined in
Section 3.2 are defined in the registry and are canonical for
the given country or region defined.
* The alphanumeric codes in Appendix X of the UN document are
_not_ defined and MUST NOT be used to form language tags. (At
the time this document was created these values match the ISO
3166 alpha-2 codes.)
o There may be at most one region subtag in a language tag.
o The subtags 'AA', 'QM'-'QZ', 'XA'-'XZ', and 'ZZ' are reserved for
private use in language tags. These subtags correspond to codes
reserved by ISO 3166 for private use. These codes MAY be used for
private use region subtags (instead of using a private-use subtag
sequence). Please refer to Section 2.5 for more information on
private use subtags.
"de-Latn-CH" represents German ('de') written using the Latin script
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('Latn') as used in Switzerland ('CH').
"sr-Latn-CS" represents Serbian ('sr') written using Latin script
('Latn') as used in Serbia and Montenegro ('CS').
"es-419" represents Spanish ('es') as used in the UN-defined Latin
America and Caribbean region ('419').
2.2.5 Variant Subtags
The following rules apply to the variant subtags:
o Variant subtags, as a collection in the IANA registry, are not
associated with any external standard. Variant subtags and their
meanings are defined by the registration process defined in
Section 3.3.
o Variant subtags MUST follow all of the other defined subtags, but
precede any extension or private-use subtag sequences.
o More than one variant MAY be used to form the language tag.
o Variant subtags MUST be registered with IANA according to the
rules in Section 3.3 of this document before being used to form
language tags. In order to distinguish variants from other types
of subtags, registrations must meet the following length and
content restrictions:
* Variant subtags that begin with a letter (a-z, A-Z) MUST be at
least five characters long.
* Variant subtags that begin with a digit (0-9) MUST be at least
four characters long.
* The maximum length of a variant subtag is eight characters
long.
"en-boont" represents the Boontling dialect of English.
"de-CH-1996" represents German as used in Switzerland and as written
using the spelling reform beginning in the year 1996 C.E.
2.2.6 Extension Subtags
The following rules apply to extensions:
o Extension subtags are separated from the other subtags defined in
this document by a single-letter subtag ("singleton"). The
singleton MUST be one allocated to a registration authority via
the mechanism described in Section 3.4 and cannot be the letter
'x', which is reserved for private-use subtag sequences.
o Note: Private-use subtag sequences starting with the singleton
subtag 'x' are described below.
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o An extension MUST follow at least a primary language subtag. That
is, a language tag cannot begin with an extension. Extensions
extend language tags, they do not override or replace them. For
example, "a-value" is not a well-formed language tag, while
"de-a-value" is.
o Each singleton subtag MUST appear at most one time in each tag
(other than as a private-use subtag). That is, singleton subtags
MUST NOT be repeated. For example, the tag "en-a-bbb-a-ccc" is
invalid because the subtag 'a' appears twice.
o Extension subtags MUST meet all of the requirements for the
content and format of subtags defined in this document.
o Extension subtags MUST meet whatever requirements are set by the
document that defines their singleton prefix and whatever
requirements are provided by the maintaining authority.
o Each extension subtag MUST be from two to eight characters long
and consist solely of letters or digits, with each subtag
separated by a single '-'.
o Each singleton MUST be followed by at least one extension subtag.
For example, the tag "tlh-a-b-foo" is invalid because the first
singleton 'a' is followed immediately by another singleton 'b'.
o Extension subtags MUST follow all language, extended language,
script, region and variant subtags in a tag.
o All subtags following the singleton and before another singleton
are part of the extension. Example: In the tag "fr-a-Latn", the
subtag 'Latn' does not represent the script subtag 'Latn' defined
in the IANA Language Subtag Registry. Its meaning is defined by
the extension 'a'.
o In the event that more than one extension appears in a single tag,
the tag SHOULD be canonicalized as described in Section 2.4.1.
For example, if the prefix singleton 'r' and the shown subtags were
defined, then the following tag would be a valid example:
"en-Latn-GB-boont-r-extended-sequence-x-private"
2.2.7 Private Use Subtags
The following rules apply to private-use subtags:
o Private-use subtags are separated from the other subtags defined
in this document by the reserved single-character subtag 'x'.
o Private-use subtags MUST follow all language, extended language,
script, region, variant, and extension subtags in the tag.
Another way of saying this is that all subtags following the
singleton 'x' MUST be considered private use. Example: The subtag
'US' in the tag "en-x-US" is a private use subtag.
o Unlike Extensions, a tag MAY consist entirely of private-use
subtags.
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o No source is defined for private use subtags. Use of private use
subtags is by private agreement and SHOULD NOT be considered part
of this document.
For example: Users who wished to utilize SIL Ethnologue for
identification might agree to exchange tags such as
"az-Arab-x-AZE-derbend". This example contains two private-use
subtags. The first is 'AZE' and the second is 'derbend'.
2.2.8 Pre-Existing RFC 3066 Registrations
Existing IANA-registered language tags from RFC 1766 and/or RFC 3066
that are not defined by additions to this document maintain their
validity. IANA will maintain these tags in the registry under either
the "grandfathered" or "redundant" type. For more information see
Appendix C.
It is important to note that all language tags formed under the
guidelines in this document were either legal, well-formed tags or
were valid for potential registration under RFC 3066.
2.2.9 Possibilities for Registration
Possibilities for registration of subtags include:
o Primary language subtags for languages not listed in ISO 639 that
are not variants of any listed or registered language, can be
registered. At the time this document was created there were no
examples of this form of subtag. Before attempting to register a
language subtag, there MUST be an attempt to register the language
with ISO 639. No language subtags will be registered for codes
that exist in ISO 639-1 or ISO 639-2, which are under
consideration by the ISO 639 maintenance or registration
authorities, or which have never been attempted for registration
with those authorities. If ISO 639 has previously rejected a
language for registration, it is reasonable to assume that there
MUST be additional very compelling evidence of need before it will
be registered in the IANA registry (to the extent that it is very
unlikely that any subtags will be registered of this type).
o Dialect or other divisions or variations within a language, its
orthography, writing system, regional variation, or historical
usage may be registered as variant subtags. An example is the
'scouse' subtag (the Scouse dialect of English).
This document leaves the decision on what subtags are appropriate or
not to the registration process described in Section 3.3.
ISO 639 defines a maintenance agency for additions to and changes in
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the list of languages in ISO 639. This agency is:
International Information Centre for Terminology (Infoterm)
Aichholzgasse 6/12, AT-1120
Wien, Austria
Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72
ISO 639-2 defines a maintenance agency for additions to and changes
in the list of languages in ISO 639-2. This agency is:
Library of Congress
Network Development and MARC Standards Office
Washington, D.C. 20540 USA
Phone: +1 202 707 6237 Fax: +1 202 707 0115
URL: http://www.loc.gov/standards/iso639
The maintenance agency for ISO 3166 (country codes) is:
ISO 3166 Maintenance Agency
c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924
The Statistics Division of the United Nations Secretariat maintains
the Standard Country or Area Codes for Statistical Use and can be
reached at:
Statistical Services Branch
Statistics Division
United Nations, Room DC2-1620
New York, NY 10017, USA
Fax: +1-212-963-0623
E-mail: statistics@un.org
URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm
2.2.10 Classes of Conformance
Implementations may wish to express their level of conformance with
the rules and practices described in this document. There are
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generally two classes of conforming implementations: "well-formed"
processors and "validating" processors. Claims of conformance SHOULD
explicitly reference one of these definitions.
An implementation that claims to check for well-formed language tags
MUST:
o Check that the tag and all of its subtags, including extension and
private-use subtags, conform to the ABNF or that the tag is on the
list of grandfathered tags.
o Check that singleton subtags that identify extensions do not
repeat. For example, the tag "en-a-xx-b-yy-a-zz" is not
well-formed.
Well-formed processors are strongly encouraged to implement the
canonicalization rules contained in Section 2.4.1.
An implementation that claims to be validating MUST:
o Check that the tag is well-formed.
o Specify the particular registry date for which the implementation
performs validation of subtags.
o Check that either the tag is a grandfathered tag, or that all
language, script, region, and variant subtags consist of valid
codes for use in language tags according to the IANA registry as
of the particular date specified by the implementation.
o Specify which, if any, extension RFCs as defined in Section 3.4
are supported, including version, revision, and date.
o For any such extensions supported, check that all subtags used in
that extension are valid.
o If the processor generates tags, it MUST do so in canonical form,
including any supported extensions, as defined in Section 2.4.1.
2.3 Choice of Language Tag
One may occasionally be faced with several possible tags for the same
body of text.
Interoperability is best served when all users use the same language
tag in order to represent the same language. If an application has
requirements that make the rules here inapplicable, then that
application risks damaging interoperability. It is STRONGLY
RECOMMENDED that users not define their own rules for language tag
choice.
Standards, protocols and applications that reference this document
normatively but apply different rules to the ones given in this
section MUST specify how the procedure varies from the one given
here.
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1. Use as precise a tag as possible, but no more specific than is
justified. For example, 'de' might suffice for tagging an email
written in German, while "de-CH-1996" is probably unnecessarily
precise for such a task.
2. Avoid using subtags that are not important for distinguishing
content in an application. For example, including the script
subtag in "en-Latn-US" is generally unnecessary, since nearly all
English texts are written in the Latin script and it is generally
not important to filter out those few that are not.
3. Use the canonical subtag from the IANA registry in preference to
any of its aliases. For example, you should use 'he' for Hebrew
in preference to 'iw'.
4. You SHOULD NOT use the 'UND' (Undetermined) language subtag to
label content, even if the language is unknown. Omitting the tag
is preferred. Some protocols may force you to give a value for
the language tag and the 'UND' subtag may be useful when matching
language tags in certain situations.
5. You SHOULD NOT use the 'MUL' (Multiple) subtag if the protocol
allows you to use multiple languages, as is the case for the
Content-Language header in HTTP.
6. You SHOULD NOT use the same variant subtag more than once within
a language tag. For example, you should not use
"en-US-boont-boont".
To ensure consistent backward compatibility, this document contains
several provisions to account for potential instability in the
standards used to define the subtags that make up language tags.
These provisions mean that no language tag created under the rules in
this document will become obsolete. In addition, tags that are in
canonical form will always be in canonical form.
2.4 Meaning of the Language Tag
The language tag always defines a language as spoken (or written,
signed or otherwise signaled) by human beings for communication of
information to other human beings. Computer languages such as
programming languages are explicitly excluded.
If a language tag B contains language tag A as a prefix, then B is
typically "narrower" or "more specific" than A. For example,
"zh-Hant-TW" is more specific than "zh-Hant".
This relationship is not guaranteed in all cases: specifically,
languages that begin with the same sequence of subtags are NOT
guaranteed to be mutually intelligible, although they may be. For
example, the tag "az" shares a prefix with both "az-Latn"
(Azerbaijani written using the Latin script) and "az-Cyrl"
(Azerbaijani written using the Cyrillic script). A person fluent in
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one script may not be able to read the other, even though the text
might be identical. Content tagged as "az" most probably is written
in just one script and thus might not be intelligible to a reader
familiar with the other script.
The relationship between the tag and the information it relates to is
defined by the standard describing the context in which it appears.
Accordingly, this section can only give possible examples of its
usage.
o For a single information object, the associated language tags
might be interpreted as the set of languages that is required for
a complete comprehension of the complete object. Example: Plain
text documents.
o For an aggregation of information objects, the associated language
tags could be taken as the set of languages used inside components
of that aggregation. Examples: Document stores and libraries.
o For information objects whose purpose is to provide alternatives,
the associated language tags could be regarded as a hint that the
content is provided in several languages, and that one has to
inspect each of the alternatives in order to find its language or
languages. In this case, the presence of multiple tags might not
mean that one needs to be multi-lingual to get complete
understanding of the document. Example: MIME
multipart/alternative.
o In markup languages, such as HTML and XML, language information
can be added to each part of the document identified by the markup
structure (including the whole document itself). For example, one
could write <span lang="FR">C'est la vie.</span> inside a
Norwegian document; the Norwegian-speaking user could then access
a French-Norwegian dictionary to find out what the marked section
meant. If the user were listening to that document through a
speech synthesis interface, this formation could be used to signal
the synthesizer to appropriately apply French text-to-speech
pronunciation rules to that span of text, instead of misapplying
the Norwegian rules.
2.4.1 Canonicalization of Language Tags
Since a particular language tag may be used in many processes,
language tags SHOULD always be created or generated in a canonical
form.
A language tag is in canonical form when:
1. The tag is well-formed according the rules in Section 2.1 and
Section 2.2.
2. None of the subtags in the language tag has a canonical_value
mapping in the IANA registry (see Section 3.1). Subtags with a
canonical_value mapping MUST be replaced with their mapping in
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order to canonicalize the tag.
3. If more than one extension subtag sequence exists, the extension
sequences are ordered into case-insensitive ASCII order by
singleton subtag.
Example: The language tag "en-A-aaa-B-ccc-bbb-x-xyz" is in canonical
form, while "en-B-ccc-bbb-A-aaa-X-xyz" is well-formed but not in
canonical form.
Example: The language tag "en-NH" (English as used in the New
Hebrides) is not canonical because the 'NH' subtag has a canonical
mapping to 'VU' (Vanuatu).
Note: Canonicalization of language tags does not imply anything about
the use of upper or lowercase letter in subtags as described in
Section 2.1. All comparisons MUST be performed in a case-insensitive
manner.
Note: the value "--" in the canonical_value field of the registry
indicates a tag or subtag that has been deprecated and for which no
replacement or canonical equivalent has been assigned. Validating
processors SHOULD NOT generate tags that include these values.
An extension MUST define any relationships that may exist between the
various subtags in the extension and thus MAY define an alternate
canonicalization scheme for the extension's subtags. Extensions MAY
define how the order of the extension's subtags are interpreted. For
example, an extension could define that its subtags are in canonical
order when the subtags are placed into ASCII order: that is,
"en-a-aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension
might define that the order of the subtags influences their semantic
meaning (so that "en-b-ccc-bbb-aaa" has a different value from
"en-b-aaa-bbb-ccc"). However, extension specifications SHOULD be
designed so that they are tolerant of the typical processes described
in Section 3.4.
2.5 Considerations for Private Use Subtags
Private-use subtags require private agreement between the parties
that intend to use or exchange language tags that use them and great
caution should be used in employing them in content or protocols
intended for general use. Private-use subtags are simply useless for
information exchange without prior arrangement.
The value and semantic meaning of private-use tags and of the subtags
used within such a language tag are not defined by this document.
The use of subtags defined in the IANA registry as having a specific
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private use meaning convey more information that a purely private use
tag prefixed by the singleton subtag 'x'. For applications this
additional information may be useful.
For example, the region subtags 'AA', 'ZZ' and in the ranges
'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) may
be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a
great deal of public, interchangeable information about the language
material (that it is Chinese in the simplified Chinese script and is
suitable for some geographic region 'XQ'). While the precise
geographic region is not known outside of private agreement, the tag
conveys far more information than an opaque tag such as "x-someLang",
which contains no information about the language subtag or script
subtag outside of the private agreement.
However, in some cases content tagged with private use subtags may
interact with other systems in a different and possibly unsuitable
manner compared to tags that use opaque, privately defined subtags,
so the choice of the best approach may depend on the particular
domain in question.
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3. IANA Considerations
This section deals with the processes and requirements necessary to
maintain the registry of subtags and extensions for use in language
tags as defined by this document and in accordance with the
requirements of RFC 2434 [15].
The language subtag registry will be maintained so that, except for
extension subtags, it is possible to validate all of the subtags that
appear in a language tag under the provisions of this document or its
revisions or successors. In addition, the meaning of the various
subtags will be unambiguous and stable over time. (The meaning of
private-use subtags, of course, is not defined by the IANA registry.)
The registry defined under this document contains a comprehensive
list of all of the subtags valid in language tags. This allows
implementers a straightforward and reliable way to validate language
tags.
3.1 Format of the IANA Language Subtag Registry
The IANA Language Subtag Registry will consist of a text file that is
machine readable in the format described in this section, plus copies
of the registration forms approved by the Language Subtag Reviewer in
accordance with the process described in Section 3.3. With the
exception of the registration forms for grandfathered and redundant
tags, no registration records will be maintained for the initial set
of subtags.
Each record in the subtag registry will consist of a series of fields
separated by the symbol "|" (%x7D) and terminated by a newline. Text
appearing after the symbol "#" (%x23) contains comments. Whitespace
surrounding fields in the file is ignored. If a field contains more
than one value, the values are separated by semicolons (%x3B).
There is a single date record at the start of the file which
indicates the most recent modification date of the file. It has two
fields: the type field is "date", and the second field is the
modification date, in the "full-date" format specified in RFC 3339
[20]. For example: 2004-06-28 represents June 28, 2004 in the
Gregorian calendar:
date | 2004-06-28
The fields in each subtag record, in order, are:
type| subtag| description| date| canonical_value|
recommended_prefix # comments
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o The character "vertical line" ("|", %x7D) delimits each of the
fields.
o Empty fields (and their separators) at the end of the record may
be omitted.
o Leading or trailing whitespace in each field is not part of the
content.
o When the type is "grandfathered" or "redundant", then the subtag
field is actually a whole tag.
o The "recommended_prefix" field is empty, except where the type is
"variant"
o The "comments" field is optional and appears only at the end of a
record, following a "number sign" ("#", %x23).
o The sequence '..' denotes a range of values. Such a range
represents all subtags of the same length that are alphabetically
within that range, including the values explicitly mentioned. For
example 'a..c' denotes the values 'a', 'b', and 'c'.
The field 'type' MUST consist of one of the following strings:
"language", "extlang", "script", "region", "variant",
"grandfathered", and "redundant" and denotes the type of subtag (or
tag, in the case of "grandfathered" and "redundant").
The field 'subtag' contains the subtag being defined.
The field 'description' contains a description of the subtag
transcribed into ASCII.
Note: Descriptions in registry entries that correspond to ISO 639,
ISO 15924, ISO 3166 or UN M.49 codes are intended only to indicate
the meaning of that identifier as defined in the source standard at
the time it was added to the registry. The description does not
replace the content of the source standard itself. The descriptions
are not intended to be the English localized names for the subtags
and localization or translation of language tag and subtag
descriptions is out of scope of this document.
The field 'date' contains the date the record was added to the
registry in the "full-date" format specified in RFC 3339 [20]. For
example: 2004-06-28 represents June 28, 2004, in the Gregorian
calendar.
The field 'canonical value' represents a canonical mapping of this
record to a subtag record of the same 'type', except for records of
type "grandfathered" and "redundant". This field SHALL NOT be
modified (except for records of type "grandfathered"): therefore a
subtag whose record contains no canonical mapping when the record is
created is a canonical form and will remain so. The 'canonical
value' field in records of type "grandfathered" and "redundant"
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contain whole language tags that are STRONGLY RECOMMENDED for use in
place of the record's value. In many cases the mappings were created
by deprecation of the tags during the period before this document was
adopted. For example, the tag "no-nyn" was deprecated in favor of
the ISO 639-1 defined language code 'nn'.
The value "--" in the 'canonical value' field means that the tag or
subtag has been deprecated and that no replacement value has been
assigned. For example, the "region" code 'BQ' (British Antarctic
Territory) was withdrawn by ISO 3166 in 1979. Although valid in
language tags, it is deprecated and validating processors SHOULD NOT
generate this subtag.
The field 'recommended prefix' is for use with registered variants
and contains a semicolon separated list of language-ranges considered
most appropriate for use with this subtag. Additional values can be
added to this field for variants only via additional registration.
Other modification of this field (such as removing or changing
values) is not permitted.
The field 'comments' may contain additional information about the
subtag, as deemed appropriate for understanding the registry and
implementing language tags using the various subtags. These values
can be changed via the registration process and no guarantee of
stability is provided.
# IANA Language Subtag Registry
# This registry lists all valid subtags for language tags
# created under RFC XXXX.
date| 2004-08-07
# language codes: ISO 639 and registered codes
# ISO 639-1 (alpha-2) codes
language| aa| Afar| 2004-07-06| |
language| ab| Abkhazian| 2004-07-06| |
language| ae| Avestan| 2004-07-06| |
language| he| hebrew| 2004-06-28| |
language| iw| hebrew| 2004-06-28| he | #note mapping
language| qaa..qtz| PRIVATE USE| 2004-07-06| |
language| raj| Rajasthani| 2004-07-06| |
language| seuss| Hypothetical Language| 2005-04-01 | |# registered language
# script codes: ISO 15924
script| Arab| Arabic| 2004-07-06| |
script| Armn| Armenian| 2004-07-06| |
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script| Bali| Balinese| 2004-07-06| |
# region codes: ISO 3166 and UN codes
# ISO 3166-1 alpha-2 codes
region| AA| PRIVATE USE| 2004-08-01| |
region| AD| Andorra| 2004-07-06| |
region| AE| United Arab Emirates| 2004-07-06| |
region| AF| Afghanistan| 2004-07-06| |
region| BQ| British Antarctic Territory | 2004-07-06 | -- | # deprecated 1979
region| CS| Serbia and Montenegro| 2003-07-23| |
region| YU| Yugoslavia| 2004-06-28| |
# United Nations M.49 numeric codes
region| 001| World| 2004-07-06| |
region| 002| Africa| 2004-07-06| |
region| 003| North America| 2004-07-06| |
region| 005| South America| 2004-07-06| |
region| 200| Czechoslovakia| 2004-07-06| | #formerly used code CS
## registered variants
variant| boont| Boontling| 2003-02-14| | en
variant| gaulish| Gaulish| 2001-05-25| | cel
variant| guoyu| Mandarin or Standard Chinese| 1999-12-18| | zh
# grandfathered from RFC 3066
grandfathered| en-GB-oed| English, Oxford English Dictionary spelling| 2003-07-09| |
grandfathered| i-ami| Amis| 1999-05-25| |
grandfathered| i-bnn| Bunun| 1999-05-25| |
grandfathered| art-lojban| Lojban| 2001-11-11|jbo | # deprecated in favor of 'jbo'
# redundant
# The following codes were registered as complete tags, but can now be
# composed of registered subtags and do not require registration.
redundant| az-Arab| Azerbaijani in Arabic script| 2003-05-30| | # use language az + script Arab
redundant| az-Cyrl| Azerbaijani in Cyrillic script| 2003-05-30| | # use language az + script Cyrl
redundant| en-boont| Boontling| 2003-02-14| | # use language en + variant boont
Figure 2: Example of the Registry Format
Maintenance of the registry requires that as new codes are assigned
by ISO 639, ISO 15924, and ISO 3166, the Language Subtag Reviewer
will evaluate each assignment, determine whether it conflicts with
existing registry entries, and submit the information to IANA for
inclusion in the registry.
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Note: The redundant and grandfathered entries together are the
complete list of tags registered under RFC 3066 [18]. The redundant
tags are those that can now be formed using the subtags defined in
Section 2.2. The grandfathered entries are those that can never be
legal under those same provisions. The items in both lists are
permanent and stable, although grandfathered items may be deprecated
over time. Refer to Appendix C for more information.
RFC 3066 tags that were deprecated prior to the adoption of this
document are part of the list of grandfathered tags and their
component subtags were not included as registered variants (although
they remain eligible for registration). For example, the tag
"art-lojban" was deprecated in favor of the language subtag 'jbo'.
The Language Subtag Reviewer MUST ensure that new subtags meet the
requirements in Section 2.3 or submit an appropriate alternate subtag
as described in that section. She or he will use the following form
to submit this information:
LANGUAGE SUBTAG REGISTRATION FORM (NEW RECORD)
Record Text:
Type:
Subtag:
Description:
Date:
Canonical Mapping:
Recommended Prefix:
Comments:
Figure 3
The field 'record text' contains the exact record that IANA is to
insert into the Language Subtag Registry. The contents of the
remaining fields must exactly match those in this field.
Whenever an entry is created or modified in the registry, the 'date'
record at the start of the registry is updated to reflect the most
recent modification date in the RFC 3339 [20] "full-date" format.
3.2 Stability of IANA Registry Entries
The stability of entries and their meaning in the registry is
critical to the long term stability of language tags. The rules in
this section guarantee that a specific language tag's meaning is
stable over time and will not change and that the choice of language
tag for specific content is also stable over time.
These rules specifically deal with how changes to codes (including
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withdrawal and deprecation of codes) maintained by ISO 639, ISO
15924, ISO 3166, and UN M.49 are reflected in the IANA Language
Subtag Registry. Assignments to the IANA Language Subtag Registry
MUST follow the following stability rules:
o Values in the fields 'type', 'subtag', 'date' and 'canonical
value' MUST NOT be changed and are guaranteed to be stable over
time.
o Values in the 'description' field MUST NOT be changed in a way
that would invalidate previously-existing tags. They may be
broadened somewhat in scope, changed to add information, or
adapted to the most common modern usage. For example, countries
occasionally change their official names: an historical example of
this would be "Upper Volta" changing to "Burkina Faso".
o Values in the field 'recommended prefix' MAY be added via the
registration process.
o Values in the field 'recommended prefix' MAY be modified, so long
as the modifications broaden the set of recommended prefixes.
That is, a recommended prefix MAY be replaced by one of its own
prefixes. For example, the prefix "en-US" could be replaced by
"en", but not by the ranges "en-Latn", "fr", or "en-US-boont".
o Values in the field 'recommended prefix' MUST NOT be removed.
o The field 'comments' MAY be added, changed, modified, or removed
via the registration process or any of the processes or
considerations described in this section.
o Codes assigned by ISO 639, ISO 15924, and ISO 3166 that do not
conflict with existing subtags of the associated type and whose
meaning is not the same as an existing subtag of the same type are
entered into the IANA registry as new records and their value is
canonical for the meaning assigned to them.
o Codes assigned by ISO 639, ISO 15924, or ISO 3166 that are
withdrawn by their respective maintenance or registration
authority remain valid in language tags. The registration process
MAY be used to add a note indicating the withdrawal of the code by
the respective standard.
o Codes assigned by ISO 639, ISO 15924, or ISO 3166 that do not
conflict with existing subtags of the associated type but which
represent the same meaning as an existing subtag of that type are
entered into the IANA registry as new records. The field
'canonical value' for that record MUST contain the existing subtag
of the same meaning
Example If ISO 3166 were to assign the code 'IM' to represent the
value "Isle of Man" (represented in the IANA registry by the UN
M.49 code '833'), '833' remains the canonical subtag and 'IM'
would be assigned '833' as a canonical value. This prevents
tags that are in canonical form from becoming non-canonical.
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Example If the tag 'enochian' were registered as a primary
language subtag and ISO 639 subsequently assigned an alpha-3
code to the same language, the new ISO 639 code would be
entered into the IANA registry as a subtag with a canonical
mapping to 'enochian'. The new ISO code can be used, but it is
not canonical.
o Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict
with existing subtags of the associated type MUST NOT be entered
into the registry. The following additional considerations apply:
* For ISO 639 codes, if the newly assigned code's meaning is not
represented by a subtag in the IANA registry, the Language
Subtag Reviewer, as described in Section 3.3, shall prepare a
proposal for entering in the IANA registry as soon as practical
a registered language subtag as an alternate value for the new
code. The form of the registered language subtag will be at
the discretion of the Language Subtag Reviewer and must conform
to other restrictions on language subtags in this document.
* For all subtags whose meaning is derived from an external
standard (i.e. ISO 639, ISO 15924, ISO 3166, or UN M.49), if a
new meaning is assigned to an existing code and the new meaning
broadens the meaning of that code, then the meaning for the
associated subtag MAY be changed to match. The meaning of a
subtag MUST NOT be narrowed, however, as this can result in an
unknown proportion of the existing uses of a subtag becoming
invalid. Note: ISO 639 MA/RA has adopted a similar stability
policy.
* For ISO 15924 codes, if the newly assigned code's meaning is
not represented by a subtag in the IANA registry, the Language
Subtag Reviewer, as described in Section 3.3, shall prepare a
proposal for entering in the IANA registry as soon as practical
a registered variant subtag as an alternate value for the new
code. The form of the registered variant subtag will be at the
discretion of the Language Subtag Reviewer and must conform to
other restrictions on variant subtags in this document.
* For ISO 3166 codes, if the newly assigned code's meaning is
associated with the same UN M.49 code as another 'region'
subtag, then the existing region subtag remains as the
canonical entry for that region and no new entry is created. A
note MAY be added to the existing region subtag indicating the
relationship to the new ISO 3166 code.
* For ISO 3166 codes, if the newly assigned code's meaning is
associated with a UN M.49 code that is not represented by an
existing region subtag, then then the Language Subtag Reviewer,
as described in Section 3.3, shall prepare a proposal for
entering the appropriate numeric UN country code as an entry in
the IANA registry.
* For ISO 3166 codes, if there is no associated UN numeric code,
then the Language Subtag Reviewer SHALL petition the UN to
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create one. If there is no response from the UN within ninety
days of the request being sent, the Language Subtag Reviewer
shall prepare a proposal for entering in the IANA registry as
soon as practical a registered variant subtag as an alternate
value for the new code. The form of the registered variant
subtag will be at the discretion of the Language Subtag
Reviewer and must conform to other restrictions on variant
subtags in this document. This situation is very unlikely to
ever occur.
o Stability provisions apply to grandfathered tags with this
exception: should all of the subtags in a grandfathered tag become
valid subtags in the IANA registry, then the grandfathered tag
MUST be marked as redundant. Note that this will not affect
language tags that match the grandfathered tag, since these tags
will now match valid generative subtag sequences. For example, if
the subtag 'gan' in the language tag "zh-gan" were to be
registered as an extended language subtag, then the grandfathered
tag "zh-gan" would be deprecated (but existing content or
implementations that use "zh-gan" would remain valid).
Language tags formed under RFC 3066 that use the region subtag 'CS'
were ambiguous, since tags produced before 2003 used that code for
the (now dissolved) country Czechoslovakia. ISO 3166 assigned this
code to the country Serbia and Montenegro in 2003 and this draft
makes that the canonical value for this subtag. To form a language
tag for the region Czechoslovakia, the UN M.49 code '200' is included
in the registry. As a practical matter, applications that encounter
the RFC 3066 tag "cs-CS" or "sk-CS" MAY wish to convert that to
"cs-200" or "sk-200" (or use one of the successor region subtags,
such as 'CZ' or 'SK'), since that is the most likely interpretation.
3.3 Registration Procedure for Subtags
The procedure given here MUST be used by anyone who wants to use a
subtag not currently in the IANA Language Subtag Registry.
Only primary language and variant subtags will be considered for
independent registration. (Subtags required for stability and
subtags required to keep the registry synchronized with ISO 639, ISO
15924, ISO 3166, and UN M.49 within the limits defined by this
document are the only exceptions to this. See Section 3.2.)
This procedure MAY also be used to register or alter the information
for the "description", "note", or "recommended prefix" fields in a
subtag's record as described in Figure 2. Changes to all other
fields in the IANA registry are NOT permitted.
If registering a new language subtag, the process starts by filling
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out the registration form reproduced below. Note that each response
is not limited in size and should take the room necessary to
adequately describe the registration.
LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester:
2. E-mail address of requester:
3. Subtag to be registered:
4. Type of Registration:
[ ] language
[ ] variant
5. Description of subtag (in English or transcribed into ASCII):
6. Intended meaning of the subtag:
7. Recommended prefix(es) of subtag (for variants):
8. Native name of the language or variation (transcribed into ASCII):
9. Reference to published description of the language (book or article):
10. Any other relevant information:
Figure 4
The subtag registration form MUST be sent to
<ietf-languages@iana.org> for a two week review period before it can
be submitted to IANA. (This is an open list. Requests to be added
should be sent to <ietf-languages-request@iana.org>.)
Variant subtags are generally registered for use with a particular
range of language tags. For example, the subtag 'boont' is intended
for use with language tags that start with the primary language
subtag "en", since Boontling is a dialect of English. Thus the
subtag 'boont' could be included in tags such as "en-Latn-boont" or
"en-US-boont". This information is stored in the "recommended
prefix" field in the registry and MUST be provided in the
registration form.
Any subtag MAY be incorporated into a variety of language tags,
according to the rules of Section 2.1, including tags that do not
match any of the recommended prefixes of the registered subtag.
(Note that this is probably a poor choice.) This makes validation
simpler and thus more uniform across implementations, and does not
require the registration of a separate subtag for the same purpose
and meaning but a different recommended prefix.
The recommended prefixes for a given registered subtag will be
maintained in the IANA registry as a guide to usage. If it is
necessary to add an additional prefix to that list for an existing
language tag, that can be done by filing an additional registration
form. In that form, the "Any other relevant information:" field
should indicate that it is the addition of an additional recommended
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prefix.
Requests to add a recommended prefix to a subtag that imply a
different semantic meaning will probably be rejected. For example, a
request to add the prefix "de" to the subtag 'nedis' so that the tag
"de-nedis" represented some German dialect would be rejected. The
'nedis' subtag represents a particular Slovenian dialect and the
additional registration would change the semantic meaning assigned to
the subtag. A separate subtag should be proposed instead.
The Language Subtag Reviewer is responsible for responding to
requests for the registration of subtags through the registration
process and is appointed by the IESG.
When the two week period has passed the Language Subtag Reviewer
either forwards the request to iana@iana.org, or rejects it because
of significant objections raised on the list or due to problems with
constraints in this document (which should be explicitly cited). The
reviewer may also extend the review period in two week increments to
permit further discussion. The reviewer must indicate on the list
whether the registration has been accepted, rejected, or extended
following each two week period.
Note that the reviewer can raise objections on the list if he or she
so desires. The important thing is that the objection must be made
publicly.
The applicant is free to modify a rejected application with
additional information and submit it again; this restarts the two
week comment period.
Decisions made by the reviewer may be appealed to the IESG [RFC 2028]
[10] under the same rules as other IETF decisions [RFC 2026] [21].
All approved registration forms are available online in the directory
http://www.iana.org/numbers.html under "languages".
Updates of registrations follow the same procedure as registrations.
The subtag reviewer decides whether to allow a new registrant to
update a registration made by someone else; normally objections by
the original registrant would carry extra weight in such a decision.
Registrations are permanent and stable. Once registered, subtags
will not be removed from the registry and will remain the canonical
method of referring to a specific language or variant. This
provision does not apply to grandfathered tags, which may become
deprecated due to registration of subtags. For example, the tag
"i-navajo" is deprecated in favor of the ISO 639-1 based subtag 'nv'.
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Note: The purpose of the "published description" in the registration
form is intended as an aid to people trying to verify whether a
language is registered or what language or language variation a
particular subtag refers to. In most cases, reference to an
authoritative grammar or dictionary of that language will be useful;
in cases where no such work exists, other well known works describing
that language or in that language may be appropriate. The subtag
reviewer decides what constitutes "good enough" reference material.
This requirement is not intended to exclude particular languages or
dialects due to the size of the speaker population or lack of a
standardized orthography. Minority languages will be considered
equally on their own merits.
3.4 Extensions and Extensions Namespace
Extension subtags are those introduced by single-letter subtags other
than 'x-'. They are reserved for the generation of identifiers which
contain a language component, and are compatible with applications
that process language tags according to this specification. For
example, they might be used to define locale identifiers, which are
generally based on language.
The structure and form of extensions are defined by this document so
that implementations can be created that are forward compatible with
applications that may be created using single-letter subtags in the
future. In addition, defining a mechanism for maintaining
single-letter subtags will lend to the stability of this document by
reducing the likely need for future revisions or updates.
IANA will maintain a registry of allocated single-letter subtags.
This registry contains the following information: letter identifier;
name; purpose; RFC defining the subtag namespace and its use; and the
name, URL, and email address of the maintaining authority.
Allocation of a single-letter subtag shall take the form of an RFC
defining the name, purpose, processes, and procedures for maintaining
the subtags. The maintaining or registering authority, including
name, contact email, discussion list email, and URL location of the
registry must be indicated clearly in the RFC. The RFC MUST specify
each of the following:
o The specification MUST reference the specific version or revision
of this document that govern its creation and MUST reference this
section of this document.
o The specification and all subtags defined by the specification
MUST follow the ABNF and other rules for the formation of tags and
subtags as defined in this document. In particular it MUST
specify that case is not significant.
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o The specification MUST specify a canonical representation.
o The specification of valid subtags MUST be available over the
Internet and at no cost.
o The specification MUST be in the public domain or available via a
royalty-free license acceptable to the IETF and specified in the
RFC.
o The specification MUST be versioned and each version of the
specification MUST be numbered, dated, and stable.
o The specification MUST be stable. That is, extension subtags,
once defined by a specification, MUST NOT be retracted or change
in meaning in any substantial way.
o IANA MUST be informed of changes to the contact information and
URL for the specification.
The determination of whether an Internet-Draft meets the above
conditions and the decision to grant or withhold such authority rests
solely with the IESG, and is subject to the normal review and appeals
process associated with the RFC process.
Extension authors are strongly cautioned that many (including most
well-formed) processors will be unaware of any special relationships
or meaning inherent in the order of extension subtags. Extension
authors SHOULD avoid subtag relationships or canonicalization
mechanisms that interfere with matching or with length restrictions
that may exist in common protocols where the extension is used. In
particular, applications may truncate the subtags in doing matching
or in fitting into limited lengths, so it is RECOMMENDED that the
most significant information be in the most significant (left-most)
subtags, and that the specification gracefully handle truncated
subtags.
When a language tag is to be used in a specific, known, protocol, it
is RECOMMENDED that that the language tag not contain extensions not
supported by that protocol. In addition, it should be noted that
some protocols may impose upper limits on the length of the strings
used to store or transport the language tag.
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4. Security Considerations
The only security issue that has been raised with language tags since
the publication of RFC 1766, which stated that "Security issues are
believed to be irrelevant to this memo", is a concern with language
identifiers used in content negotiation - that they may be used to
infer the nationality of the sender, and thus identify potential
targets for surveillance.
This is a special case of the general problem that anything you send
is visible to the receiving party. It is useful to be aware that
such concerns can exist in some cases.
The evaluation of the exact magnitude of the threat, and any possible
countermeasures, is left to each application protocol.
Although the specification of valid subtags for an extension MUST be
available over the Internet, implementations SHOULD NOT mechanically
depend on it being always accessible, to prevent denial-of-service
attacks.
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5. Character Set Considerations
The syntax in this document requires that language tags use only the
characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most
character sets, so presentation of language tags should not have any
character set issues.
Rendering of characters based on the content of a language tag is not
addressed in this memo. Historically, some languages have relied on
the use of specific character sets or other information in order to
infer how a specific character should be rendered (notably this
applies to language and culture specific variations of Han ideographs
as used in Japanese, Chinese, and Korean). When language tags are
applied to spans of text, rendering engines may use that information
in deciding which font to use in the absence of other information,
particularly where languages with distinct writing traditions use the
same characters.
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6. Changes from RFC 3066
The main goals for this revision of language tags were the following:
*Compatibility.* All valid RFC 3066 language tags (including those
in the IANA registry) remain valid in this specification. Thus
there is complete backward compatibility of this specification with
existing content. In addition, this document defines language tags
in such as way as to ensure future compatibility, and processors
based solely on the RFC 3066 ABNF (such as those described in XML
Schema version 1.0) will be able to process tags described by this
document.
*Stability.* Because of the changes in underlying ISO standards, a
valid RFC 3066 language tag may become invalid (or have its meaning
change) at a later date. With so much of the world's computing
infrastructure dependent on language tags, this is simply
unacceptable: it invalidates content that may have an extensive
shelf-life. In this specification, once a language tag is valid, it
remains valid forever. Previously, there was no way to determine
when two tags were equivalent. This specification provides a stable
mechanism for doing so, through the use of canonical forms. These
are also stable, so that implementations can depend on the use of
canonical forms to assess equivalency.
*Validity.* The structure of language tags defined by this document
makes it possible to determine if a particular tag is well-formed
without regard for the actual content or "meaning" of the tag as a
whole. This is important because the registry and underlying
standards change over time. In addition, it must be possible to
determine if a tag is valid (or not) for a given point in time in
order to provide reproducible, testable results. This process must
not be error-prone; otherwise even intelligent people will generate
implementations that give different results. This specification
provides for that by having a single data file, with specific
versioning information, so that the validity of language tags at any
point in time can be precisely determined (instead of interpolating
values from many separate sources).
*Extensibility.* It is important to be able to differentiate between
written forms of language -- for many implementations this is more
important than distinguishing between spoken variants of a language.
Languages are written in a wide variety of different scripts, so this
document provides for the generative use of ISO 15924 script codes.
Like the generative use of ISO language and country codes in RFC
3066, this allows combinations to be produced without resorting to
the registration process. The addition of UN codes provides for the
generation of language tags with regional scope, which is also
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required for information technology.
The recast of the registry from containing whole language tags to
subtags is a key part of this. An important feature of RFC 3066 was
that it allowed generative use of subtags. This allows people to
meaningfully use generated tags, without the delays in registering
whole tags, and the burden on the registry of having to supply all of
the combinations that people may find useful.
Because of the widespread use of language tags, it is potentially
disruptive to have periodic revisions of the core specification,
despite demonstrated need. The extension mechanism provides for a
way for independent RFCs to define extensions to language tags.
These extensions have a very constrained, well-defined structure to
prevent extensions from interfering with implementations of language
tags defined in this document. The document also anticipates
features of ISO 639-3 with the addition of the extlang subtags. The
use and definition of private use tags has also been modified, to
allow people to move as much information as possible out of private
use tags, and into the regular structure. The goal is to
dramatically reduce the need to produce a revision of this document
in the future.
The specific changes in this document to meet these goals are:
o Defines the ABNF and rules for subtags so that the category of all
subtags can be determined without reference to the registry.
o Adds the concept of well-formed vs. validating processors,
defining the rules by which an implementation can claim to be one
or the other.
o Changes the IANA language tag registry to a language subtag
registry that provides a complete list of valid subtags in the
IANA registry. This allows for robust implementation and ease of
maintenance. The language subtag registry becomes the canonical
source for forming language tags.
o Provides a process that guarantees stability of language tags, by
handling reuse of values by ISO 639, ISO 15924, and ISO 3166 in
the event that they register a previously used value for a new
purpose.
o Allows ISO 15924 script code subtags and allows them to be used
generatively. Adds the concept of a variant subtag and allows
variants to be used generatively. Adds the ability to use a class
of UN tags as regions.
o Defines the private-use tags in ISO 639, ISO 15924, and ISO 3166
as the mechanism for creating private-use language, script, and
region subtags respectively.
o Adds a well-defined extension mechanism.
o Defines an extended language subtag, possibly for use with certain
anticipated features of ISO 639-3.
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Ed Note: The following items are provided for the convenience of
reviewers and will be removed from the final document.
Changes between draft-phillips-langtags-10 and this version are:
o Expunged the terminology "language range", since that section goes
with matching (A.Phillips, M.Davis)
o Added text describing the handling of existing RFC 3066 registry
entries that were deprecated prior to the adoption of this
document. These tags are now grandfathered. (A.Phillips,
D.Ewell)
o Modified the conversion rules for the registry (Appendix C) to
refer to the chairs, the LTRU mail list and so forth (A.Phillips)
o Added text to allow tags and subtags to be deprecated using the
canonical value "--". This is applied to codes withdrawn by ISO
639 MA and ISO 3166 MA, for example. (F.Ellerman, D.Ewell)
7. References
[1] International Organization for Standardization, "ISO
639-1:2002, Codes for the representation of names of languages
-- Part 1: Alpha-2 code", ISO Standard 639, 2002.
[2] International Organization for Standardization, "ISO 639-2:1998
- Codes for the representation of names of languages -- Part 2:
Alpha-3 code - edition 1", August 1988.
[3] ISO TC46/WG3, "ISO 15924:2003 (E/F) - Codes for the
representation of names of scripts", January 2004.
[4] International Organization for Standardization, "Codes for the
representation of names of countries, 3rd edition",
ISO Standard 3166, August 1988.
[5] Statistical Division, United Nations, "Standard Country or Area
Codes for Statistical Use", UN Standard Country or Area Codes
for Statistical Use, Revision 4 (United Nations publication,
Sales No. 98.XVII.9, June 1999.
[6] ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory
Committee: Working principles for ISO 639 maintenance", March
2000,
<http://www.loc.gov/standards/iso639-2/iso639jac_n3r.html>.
[7] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021
and RFC 822", RFC 1327, May 1992.
[8] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
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the Format of Internet Message Bodies", RFC 1521, September
1993.
[9] Alvestrand, H., "Tags for the Identification of Languages",
RFC 1766, March 1995.
[10] Hovey, R. and S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
[11] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[12] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word
Extensions: Character Sets, Languages, and Continuations",
RFC 2231, November 1997.
[13] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[14] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[15] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[16] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[17] Carpenter, B., Baker, F. and M. Roberts, "Memorandum of
Understanding Concerning the Technical Work of the Internet
Assigned Numbers Authority", RFC 2860, June 2000.
[18] Alvestrand, H., "Tags for the Identification of Languages",
BCP 47, RFC 3066, January 2001.
[19] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003.
[20] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[21] <http://www.ietf.org/rfc/rfc2026.txt>
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Authors' Addresses
Addison Phillips (editor)
Quest Software
Email: addison.phillips@quest.com
Mark Davis (editor)
IBM
Email: mark.davis@us.ibm.com
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Appendix A. Acknowledgements
Any list of contributors is bound to be incomplete; please regard the
following as only a selection from the group of people who have
contributed to make this document what it is today.
The contributors to RFC 3066 and RFC 1766, the precursors of this
document, made enormous contributions directly or indirectly to this
document and are generally responsible for the success of language
tags.
The following people (in alphabetical order) contributed to this
document or to RFCs 1766 and 3066:
Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet,
Nathaniel Borenstein, Eric Brunner, Sean M. Burke, Jeremy Carroll,
John Clews, Jim Conklin, Peter Constable, John Cowan, Mark Crispin,
Dave Crocker, Martin Duerst, Frank Ellerman, Michael Everson, Doug
Ewell, Ned Freed, Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn,
Joel Halpren, Elliotte Rusty Harold, Paul Hoffman, Richard Ishida,
Olle Jarnefors, Kent Karlsson, John Klensin, Alain LaBonte, Eric
Mader, Keith Moore, Chris Newman, Masataka Ohta, George Rhoten,
Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto Stolz, Tex
Texin, Andrea Vine, Rhys Weatherley, Misha Wolf, Francois Yergeau and
many, many others.
Very special thanks must go to Harald Tveit Alvestrand, who
originated RFCs 1766 and 3066, and without whom this document would
not have been possible. Special thanks must go to Michael Everson,
who has served as language tag reviewer for almost the complete
period since the publication of RFC 1766. Special thanks to Doug
Ewell, for his production of the first complete subtag registry, and
his work in producing a test parser for verifying language tags.
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Appendix B. Examples of Language Tags (Informative)
Simple language subtag:
de (German)
fr (French)
ja (Japanese)
i-enochian (example of a grandfathered tag)
Language subtag plus Script subtag:
zh-Hant (Traditional Chinese)
en-Latn (English written in Latin script)
sr-Cyrl (Serbian written with Cyrillic script)
Language-Script-Region:
zh-Hans-CN (Simplified Chinese for the PRC)
sr-Latn-CS (Serbian, Latin script, Serbia and Montenegro)
Language-Script-Region-Variant:
en-Latn-US-boont (Boontling dialect of English)
de-Latn-CH-1996 (German written in Latin script for Switzerland
using the orthography of 1996)
Language-Region:
de-DE (German for Germany)
zh-SG (Chinese for Singapore)
cs-200 (Czech for Czechoslovakia)
sr-CS (Serbian for Serbia and Montenegro)
es-419 (Spanish for Latin America and Caribbean region using the
UN region code)
Other Mixtures:
en-boont (Boontling dialect of English)
private-use mechanism:
de-CH-x-phonebk
az-Arab-x-AZE-derbend
Extended language subtags (examples ONLY: extended languages must be
defined by revision or update to this document):
zh-min
zh-min-nan-Hant-CN
Private-use subtags:
x-whatever (private use using the singleton 'x')
qaa-Qaaa-QM-x-southern (all private tags)
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de-Qaaa (German, with a private script)
de-Latn-QM (German, Latin-script, private region)
de-Qaaa-DE (German, private script, for Germany)
Tags that use extensions (examples ONLY: extensions must be defined
by revision or update to this document or by RFC):
en-US-u-islamCal
zh-CN-a-myExt-x-private
en-a-myExt-b-another
Some Invalid Tags:
de-419-DE (two region tags)
a-DE (use of a single character subtag in primary position; note
that there are a few grandfathered tags that start with "i-" that
are valid)
ar-a-aaa-b-bbb-a-ccc (two extensions with same single letter
prefix)
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Appendix C. Conversion of the RFC 3066 Language Tag Registry
Upon publication of this document as a BCP, the existing IANA
language tag registry must be converted into the new subtag registry.
This section defines the process for performing this conversion.
The impact on the IANA maintainers of the registry of this conversion
will be a small increase in the frequency of new entries. The
initial set of records represents no impact on IANA, since the work
to create it will be performed externally.
When this document is published, an email will be sent by the
chair(s) of the LTRU working group to the LTRU and ietf-languages
mail lists advising of the impending conversion of the registry. In
that notice, the chair(s) will provide a URL whose referred content
is the proposed IANA Language Subtag Registry following conversion.
There will be a Last Call period of not less than four weeks for
comments and corrections to be discussed on the
ietf-languages@iana.org mail list. Changes as a result of comments
will not restart the Last Call period. At the end of the period, the
chair(s) will forward the URL to IANA, which will post the new
registry on-line.
Tags that are currently deprecated will be maintained as
grandfathered entries. The record for the grandfathered entry will
contain a note indicating that the entry is 'deprecated' and reason
for the deprecation. For example, the tag "art-lojban" is deprecated
and will be placed in the grandfathered section.
Tags that are not deprecated that consist entirely of subtags that
are valid under this document and which have the correct form and
format for tags defined by this document are superseded by this
document. Such tags are placed in the 'redundant' section of the
registry. For example, zh-Hant is now defined by this document.
Tags that contain subtags which are consistent with registration
under the guidelines in this document will have a new subtag
registration created for each eligible subtag. If all of the subtags
in the original tag are fully defined by the resulting registrations
or by this document, then the original tag is superseded by this
document. Such tags are placed in the 'redundant' section of the
registry. For example, en-boont will result in a new subtag "boont"
and the RFC 3066 registered tag 'en-boont' placed in the redundant
section of the registry.
Tags that contain one or more subtags that do not match the valid
registration pattern and which are not otherwise defined by this
document are marked as 'grandfathered' by this document.
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There will be a reasonable period in which the community may comment
on the proposed list entries, which SHALL be no less than four weeks
in length. At the completion of this period, the chair(s) will
notify iana@iana.org and the ltru and ietf-languages mail lists that
the task is complete and forward the necessary materials to IANA for
publication.
Registrations that are in process under the rules defined in RFC 3066
MAY be completed under the former rules, at the discretion of the
language tag reviewer. Any new registrations submitted after the
request for conversion of the registry MUST be rejected.
All existing RFC 3066 language tag registrations will be maintained
in perpetuity.
Users of tags that are grandfathered should consider registering
appropriate subtags in the IANA subtag registry (but are not required
to).
Where two subtags have the same meaning, the priority of which to
make canonical SHALL be the following:
o As of the date of acceptance of this document as a BCP, if a code
exists in the associated ISO standard and it is not deprecated or
withdrawn as of that date, then it has priority.
o Otherwise, the earlier-registered tag in the associated ISO
standard has priority.
UN numeric codes assigned to 'macro-geographical (continental)' or
sub-regions not associated with an assigned ISO 3166 alpha-2 code are
defined in the IANA registry and are valid for use in language tags.
These codes MUST be added to the initial version of the registry.
The UN numeric codes for 'economic groupings' or 'other groupings',
and the alphanumeric codes in Appendix X of the UN document MUST NOT
be added to the registry.
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Phillips & Davis Expires September 11, 2005 [Page 44]
