Network Working Group H. Alvestrand
Request for Comments: 3066 Cisco Systems
BCP: 47 January 2001
Category: Best Current Practice
Tags for the Identification of Languages
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document describes a language tag for use in cases where it is
desired to indicate the language used in an information object, how
to register values for use in this language tag, and a construct for
matching such language tags.
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 information.
In some contexts, it is possible to have information available in
more than one language, or it might be possible to provide tools
(such as dictionaries) to assist in the understanding of a language.
Also, many types of information processing require knowledge of the
language in which information is expressed in order for that process
to be performed on the information; for example spell-checking,
computer-synthesized speech, Braille, or high-quality print
One means of indicating the language used is by labeling the
information content with an identifier for the language that is used
in this information content.
Alvestrand Best Current Practice [Page 1]RFC 3066 Tags for Identification of Languages January 2001
This document specifies an identifier mechanism, a registration
function for values to be used with that identifier mechanism, and a
construct for matching against those values.
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].
2. The Language tag2.1 Language tag syntax
The language tag is composed of one or more parts: A primary language
subtag and a (possibly empty) series of subsequent subtags.
The syntax of this tag in ABNF [RFC 2234] is:
Language-Tag = Primary-subtag *( "-" Subtag )
Primary-subtag = 1*8ALPHA
Subtag = 1*8(ALPHA / DIGIT)
The productions ALPHA and DIGIT are imported from RFC 2234; they
denote respectively the characters A to Z in upper or lower case and
the digits from 0 to 9. The character "-" is HYPHEN-MINUS (ABNF:
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. For instance, [ISO 3166] recommends that
country codes are capitalized (MN Mongolia), while [ISO 639]
recommends that language codes are written in lower case (mn
2.2 Language tag sources
The namespace of language tags is administered by the Internet
Assigned Numbers Authority (IANA) [RFC 2860] according to the rules
in section 3 of this document.
The following rules apply to the primary subtag:
- All 2-letter subtags are interpreted according to assignments found
in ISO standard 639, "Code for the representation of names of
languages" [ISO 639], or assignments subsequently made by the ISO
639 part 1 maintenance agency or governing standardization bodies.
(Note: A revision is underway, and is expected to be released as
Alvestrand Best Current Practice [Page 2]RFC 3066 Tags for Identification of Languages January 2001
- All 3-letter subtags are interpreted according to assignments found
in ISO 639 part 2, "Codes for the representation of names of
languages -- Part 2: Alpha-3 code [ISO 639-2]", or assignments
subsequently made by the ISO 639 part 2 maintenance agency or
governing standardization bodies.
- The value "i" is reserved for IANA-defined registrations
- The value "x" is reserved for private use. Subtags of "x" shall
not be registered by the IANA.
- Other values shall not be assigned except by revision of this