draft Language Tag August 94
Tags for the identification of languages
Fri Aug 5 14:21:43 MET DST 1994
Harald Tveit Alvestrand
UNINETT
Harald.T.Alvestrand@uninett.no
Abstract
This document describes a language tag for use in cases where it
is desired to indicate the language used in an information object.
It also defines a Content-language: header, for use in the case
where one desires to indicate the language of something that has
RFC-822-like headers, like MIME body parts or Web documents, and a
new parameter to the Multipart/Alternative type, to aid in the
usage of the Content-Language: header.
Status of this Memo
This draft document is being circulated for comment.
If consensus is reached it may be submitted to the RFC editor as a
Proposed Standard protocol specificiation.
Please send comments to the author, or to the MAILEXT mailing list
<mailext@cs.wisc.edu>
The following text is required by the Internet-draft rules:
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its
Areas, and its Working Groups. Note that other groups may also
distribute working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
Alvestrand Expires Feb 95 [Page 1]
=0C
draft Language Tag August 94
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use
Internet Drafts as reference material or to cite them other than
as a "working draft" or "work in progress."
Please check the I-D abstract listing contained in each Internet
Draft directory to learn the current status of this or any other
Internet Draft.
The filename of this document is draft-mailext-lang-tag-01.txt
Alvestrand Expires Feb 95 [Page 2]
=0C
draft Language Tag August 94
1. Introduction
There are a number of languages spoken by human beings in this
world.
A great number of these people would prefer to have information
presented in a language that they understand.
In some contexts, it is possible to have information in more than
one language, or it might be possible to provide tools for
assisting in the understanding of a language (like dicationaries).
A prerequisite for any such function is a means of labelling the
information content with an identifier for the language in which
is is written.
In the tradition of solving only problems that we think we
understand, this document specifies an identifier mechanism, and
one possible use for it.
2. The Language tag
The language tag is composed of 1 or more parts: A main language
tag and a (possibly empty) series of subtags.
The syntax of this tag in RFC-822 EBNF is:
Language-Tag =3D Tag-List
Tag-List =3D Tag-Component *[ '-', Tag-List ]
Tag-Component =3D 1*8ALPHA
Whitespace is not allowed within the tag.
All tags are to be treated as case insensitive; there exist
conventions for capitalization of some of them, but these should
not be taken to carry meaning.
The namespace of language tags and subtags is administered by the
IANA. The following registrations are predefined:
In the language tag:
Alvestrand Expires Feb 95 [Page 3]
=0C
draft Language Tag August 94
- All 2-letter codes are interpreted according to ISO 639.
- The value "i" is reserved for IANA-defined registrations
- The value "x" is reserved for private use. Subtags of "X"
will not be registered by the IANA.
- Other values cannot be assigned except by updating this
standard.
The reason for reserving all other tags is to be open towards new
revisions of ISO 639; the use of "i" and "x" is the minimum we can
do here to be able to extend the mechanism to meet our
requirements.
In the first subtag:
- All 2-letter codes are interpreted as ISO 3166 country codes,
according to the rules laid down in ISO 639.
- Codes of 3 to 8 letters may be registered with the IANA by
anyone who feels a need for it. IANA has the right to reject
registrations that are felt to be misleading.
The information in the subtag may for instance be:
- Country identification, such as en-US (this usage is
described in ISO 639)
- Dialect or variant information, such as no-NYNORSK or en-
COCKNEY
- Languages not listed in ISO 639 that are not variants of any
listed language, which can be registered with the i- prefix,
such as i-cherokee
- Script variations, such as az-arabic and az-cyrillic
In the second and subsequent subtag, any value can be registered.
Alvestrand Expires Feb 95 [Page 4]
=0C
draft Language Tag August 94
NOTE: The ISO 639/ISO 3166 convention is that language names are
written in lower case, while country codes are written in upper
case. This convention is recommended, but not enforced; the tags
are case insensitive.
NOTE: ISO 639 defines a registration authority for additions to
and changes in the list of languages in ISO 639. This authority
is:
International Information Centre for Terminology (Infoterm)
P.O. Box 130
A-1021 Wien
Austria
Phone: +43 1 26 75 35 Ext. 312
Fax: +43 1 216 32 72
The following codes have been added in 1989 (nothing later): ug
(Uigur), iu (Inuktitut, also called Eskimo), za (Zhuang), he
(Hebrew, replacing iw), yi (Yiddish, replacing ji), and id
(Indonesian, replacing in).
NOTE: The registration agency for ISO 3166 (country codes) is:
ISO 3166 Maintenance Agency Secretariat
c/o DIN Deutches Institut F=FCr Normung
Burggrafenstrasse 6
Postfach 1107
D-10787 Berlin
Germany
Phone: +49 30 26 01 320
Fax: +49 30 26 01 231
The codes AA, QM-QZ, XA-XZ and ZZ are reserved by ISO 3166 as
user-assigned codes.
2.1. Meaning of the language tag
The language tag always defines a language as spoken (or written)
by human beings for communication of information to other human
beings. Computer languages are explicitly excluded.
There is no guaranteed relationship between languages that start
Alvestrand Expires Feb 95 [Page 5]
=0C
draft Language Tag August 94
out with the same series of tags; especially, they are NOT
guraranteed to be mutually comprehensible, although this will
sometimes be the case.
Applications should always treat language tags as a single token;
the division into subtags is an administrative mechanism, not a
navigation aid.
The relationship between the tag and the information it relates to
is defined by the standard describing the context in which it
appears. So, this section can only give possible examples of its
usage.
- For a single information object, it should be taken as the
set of languages that is required for a complete
comprehension of the complete object. Example: Simple text.
- For an aggregation of information objects, it should be taken
as the set of languages used inside components of that
aggregation. Examples: Document stores and libraries.
- For information objects whose purpose in life is providing
alternatives, it should be regarded as a hint that the
material inside 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, multiple languages
need not mean that one needs to be multilingual to get
complete understanding of the document. Example: MIME
multipart/alternative.
- It would be possible to define (for instance) an SGML DTD
that defines a <LANG xx> tag for indicating that following or
contained text is written in this language, such that one
could write "<LANG FR>C'est la vie</LANG>"; the Norwegian-
speaking user could then access a French-Norwegian dictionary
to find out what the quote meant.
3. The Content-language header
The RFC-822 ABNF of the Language header is:
Language-Header =3D "Content-Language" ":" 1#Language-tag
Alvestrand Expires Feb 95 [Page 6]
=0C
draft Language Tag August 94
Note that the Language-Header is allowed to list several languages
in a comma-separated list.
Whitespace is allowed, which means also that one can place
parenthesized comments anywhere in the language sequence.
3.1. Examples of Content-language values
NOTE: NONE of the subtags shown in this document have actually
been assigned; they are used for illustration purposes only.
Norwegian official document, with parallel text in both official
versions of Norwegian. (Both versions are readable by all
Norwegians).
Content-Type: multipart/alternative; differences=3Dcontent-
language
Content-Language: no-nynorsk, no-bokmaal
Voice recording from the London docks
Content-type: audio/basic
Content-Language: en-cockney
Document in Sami, which does not have an ISO 639 code, and is
spoken in several countries, but with about half the speakers in
Norway, with six different, mutually incomprehensible dialects:
Content-type: text/plain; charset=3Diso-8859-10
Content-Language: i-sami-no (North Sami)
An English-French dictionary
Content-type: application/dictionary
Content-Language: en, fr (This is a dictionary)
An official EC document (in a few of its official languages)
Content-type: multipart/alternative
Content-Language: en, fr, de, da, el, it
An excerpt from Star Trek
Alvestrand Expires Feb 95 [Page 7]
=0C
draft Language Tag August 94
Content-type: video/mpeg
Content-Language: x-klingon
4. Use of Content-Language with Multipart/Alternative
When using the Multipart/Alternative body part of MIME, it is
possible to have the body parts giving the same information
content in different languages. In this case, one should put a
Content-Language header on each of the body parts, and a summary
Content-Language header onto the Multipart/Alternative itself.
4.1. The differences parameter to multipart/alternative
As defined in RFC 1541, Multipart/Alternative only has one
parameter: boundary.
The common usage of Multipart/Alternative is to have more than one
format of the same message (f.ex. PostScript and ASCII).
The use of language tags to differentiate between different
alternatives will certainly not lead all MIME UAs to present the
most sensible body part as default.
Therefore, a new parameter is defined, to allow the configuration
of MIME readers to handle language differences in a sensible
manner.
Name: Differences
Value: One or more of
Content-Type
Content-Language
Further values can be registered with IANA; it must be the name of
a header for which a definition exists in a published document.
If not present, Differences=3DContent-Type is assumed.
The intent is that the MIME reader can look at these headers of
the message component to do an intelligent choice of what to
present to the user, based on knowledge about the user preferences
and capabilities.
(The intent of having registration with IANA of the fields used in
Alvestrand Expires Feb 95 [Page 8]
=0C
draft Language Tag August 94
this context is to maintain a list of usages that a mail UA may
expect to see, not to reject usages)
(NOTE: The MIME specification [RFC 1521], section 7.2, states that
headers not beginning with "Content-" are generally to be ignored
in body parts. People defining a header for use with
"differences=3D" should take note of this)
The mechanism for deciding which body part to present is outside
the scope of this document.
MIME EXAMPLE:
Content-Type: multipart/alternative; differences=3DContent-Language;
boundary=3D"limit"
Content-Language: en, fr, de
--limit
Content-Language: fr
Le renard brun et agile saute par dessus le chien paresseux
--limit
Content-Language: de
Content-Type: text/plain; charset=3Diso-8859-1
Content-Transfer-encoding: 8bit
Der schnelle braune Fuchs h=FCpft =FCber den faulen Hund
--limit
Content-Language: en
The quick brown fox jumps over the lazy dog
--limit--
When composing a message, the choice of sequence may be somewhat
arbitary. However, non-MIME mail readers will show the first body
part first, meaning that this should most likely be the language
understood by most of the recipients.
5. IANA registration procedure for language tags
Any language tag must start with an existing tag, and extend it.
Alvestrand Expires Feb 95 [Page 9]
=0C
draft Language Tag August 94
This registration form should be used by anyone who wants to use a
language tag not defined by ISO or IANA.
----------------------------------------------------------------------
LANGUAGE TAG REGISTRATION FORM
Name of requester :
E-mail address of requester:
Tag to be registered :
English name of language :
Native name of language (in ASCII):
Reference to published description of the language (book or article):
----------------------------------------------------------------------
The language form must be sent to language-review@uninett.no for a
2-week review period before submitting it to IANA. (This is an
open list. Requests to be added should be sent to language-review-
request@uninett.no. General language discussions are not
appropriate for this list)
The completed form should then be sent to IANA@ISI.EDU; all
registered forms are available online in the directory
ftp://ftp.iana.isi.edu/registrations/languages/
(NOTE: The IANA may suggest alternative text here).
The IANA is free to reject registrations where it feels, based on
list feedback, that information is lacking, or that the tag name
suggests something different from the language referenced.
6. Security considerations
Security considerations are not considered in this memo
7. Character set considerations
Codes are always expressed using US-ASCII (a-z).
The issue of deciding upon the rendering of a character set based
on the language encoding is not addressed in this memo; however,
Alvestrand Expires Feb 95 [Page 10]
=0C
draft Language Tag August 94
the author cautions against thinking that such a decision can be
made correctly for all cases unless means of switching language in
the middle of a text are defined (for example, a rendering engine
that decides font based on Japanese or Chinese language will fail
to work when a mixed Japanese-Chinese text is encountered)
8. Gatewaying considerations
RFC 1327 defines a Language: header. This header is not
recommended now, because it is defined to be a single 2-letter
language code, and the X.400 header it is supposed to gateway is a
list of language codes.
It is suggested that RFC 1327 be updated to produce the Content-
Language: header, and to turn this header into the ISO/CCITT
specified Language components rather than the RFC-822-headers
heading extension.
9. References
[ISO 639]
ISO 639:1988 (E/F) - Code for the representation of names of
languages - The International Organization for
Standardization, 1st edition, 1988 17 pages Prepared by
ISO/TC 37 - Terminology (principles and coordination)
[ISO 3166]
ISO 3166:1988 (E/F) - Codes for the representation of names
of countries - The International Organization for
Standardization, 3rd edition, 1988-08-15
[RFC 1521]
MIME Part One: Mechanisms for Specifying and Describing the
Format of Internet Message Bodies - Borenstein and Freed -
September 1993
[RFC 1327]
Mapping between X.400(1988) / ISO 10021 and RFC 822 - Kille -
Alvestrand Expires Feb 95 [Page 11]
=0C
draft Language Tag August 94
May 1992
10. Change log Changes from draft-ietf-lang-tag-02.txt:
Clarified that a language tag is a single token
Changes from draft-alvestrand-language-tag-00:
IANA registration form added
IANA-reserved tag changed from "IANA" to "I", in order to
avoid clashing with possible ISO 4-letter codes
Separated "tag" definition from "header" definition
Info on ISO 639 registration office added
Created a multi-level tag, rather than strict two-level
Added examples of SGML usage
Lots of small nits fixed
Alvestrand Expires Feb 95 [Page 12]
=0C
