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rfc:rfc3066

Network Working Group H. Alvestrand Request for Comments: 3066 Cisco Systems BCP: 47 January 2001 Obsoletes: 1766 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 Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 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.

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 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
 renderings.
 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 tag

2.1 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:
 %x2D).
 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
 Mongolian).

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:
  1. 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

   ISO 639-1:2000)
  1. 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.
  1. The value "i" is reserved for IANA-defined registrations
  1. The value "x" is reserved for private use. Subtags of "x" shall

not be registered by the IANA.

  1. Other values shall not be assigned except by revision of 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 immediate
 requirements.
 The following rules apply to the second subtag:
  1. All 2-letter subtags are interpreted as ISO 3166 alpha-2 country

codes from [ISO 3166], or subsequently assigned by the ISO 3166

   maintenance agency or governing standardization bodies, denoting
   the area to which this language variant relates.
  1. Tags with second subtags of 3 to 8 letters may be registered with

IANA, according to the rules in chapter 5 of this document.

  1. Tags with 1-letter second subtags may not be assigned except after

revision of this standard.

 There are no rules apart from the syntactic ones for the third and
 subsequent subtags.
 Tags constructed wholly from the codes that are assigned
 interpretations by this chapter do not need to be registered with
 IANA before use.
 The information in a subtag may for instance be:
  1. Country identification, such as en-US (this usage is described in

ISO 639)

  1. Dialect or variant information, such as en-scouse

Alvestrand Best Current Practice [Page 3] RFC 3066 Tags for Identification of Languages January 2001

  1. 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-

   tsolyani
  1. Region identification, such as sgn-US-MA (Martha's Vineyard Sign

Language, which is found in the state of Massachusetts, US)

 This document leaves the decision on what tags are appropriate or not
 to the registration process described in section 3.
 ISO 639 defines a maintenance agency for additions to and changes in
 the list of languages in ISO 639.  This agency 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
 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 Secretariat
      c/o DIN Deutsches Institut fuer Normung
      Burggrafenstrasse 6
      Postfach 1107
      D-10787 Berlin
      Germany
      Phone: +49 30 26 01 320
      Fax:   +49 30 26 01 231
      URL: http://www.din.de/gremien/nas/nabd/iso3166ma/
 ISO 3166 reserves the country codes AA, QM-QZ, XA-XZ and ZZ as user-
 assigned codes.  These MUST NOT be used to form language tags.

Alvestrand Best Current Practice [Page 4] RFC 3066 Tags for Identification of Languages January 2001

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 if all users send the same tag, and
 use the same tag for the same language for all documents.  If an
 application has requirements that make the rules here inapplicable,
 the application protocol specification MUST specify how the procedure
 varies from the one given here.
 The text below is based on the set of tags known to the tagging
 entity.
 1. Use the most precise tagging known to the sender that can be
    ascertained and is useful within the application context.
 2. When a language has both an ISO 639-1 2-character code and an ISO
    639-2 3-character code, you MUST use the tag derived from the ISO
    639-1 2-character code.
 3. When a language has no ISO 639-1 2-character code, and the ISO
    639-2/T (Terminology) code and the ISO 639-2/B (Bibliographic)
    code differ, you MUST use the Terminology code.  NOTE: At present,
    all languages for which there is a difference have 2-character
    codes, and the displeasure of developers about the existence of 2
    code sets has been adequately communicated to ISO.  So this
    situation will hopefully not arise.
 4. When a language has both an IANA-registered tag (i-something) and
    a tag derived from an ISO registered code, you MUST use the ISO
    tag.  NOTE: When such a situation is discovered, the IANA-
    registered tag SHOULD be deprecated as soon as possible.
 5. You SHOULD NOT use the UND (Undetermined) code unless the protocol
    in use forces you to give a value for the language tag, even if
    the language is unknown.  Omitting the tag is preferred.
 6. You SHOULD NOT use the MUL (Multiple) tag if the protocol allows
    you to use multiple languages, as is the case for the Content-
    Language:  header.
 NOTE: In order to avoid versioning difficulties in applications such
 as that of RFC 1766, the ISO 639 Registration Authority Joint
 Advisory Committee (RA-JAC) has agreed on the following policy
 statement:

Alvestrand Best Current Practice [Page 5] RFC 3066 Tags for Identification of Languages January 2001

   "After the publication of ISO/DIS 639-1 as an International
   Standard, no new 2-letter code shall be added to ISO 639-1 unless a
   3-letter code is also added at the same time to ISO 639-2.  In
   addition, no language with a 3-letter code available at the time of
   publication of ISO 639-1 which at that time had no 2-letter code
   shall be subsequently given a 2-letter code."
 This will ensure that, for example, a user who implements "hwi"
 (Hawaiian), which currently has no 2-letter code, will not find his
 or her data invalidated by eventual addition of a 2-letter code for
 that language."

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.  There is no
 guaranteed relationship between languages whose tags begin with the
 same series of subtags; specifically, they are NOT guaranteed to be
 mutually intelligible, although it will sometimes be the case that
 they are.
 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.
  1. For a single information object, it could be taken as the set of

languages that is required for a complete comprehension of the

   complete object.
   Example: Plain text documents.
  1. 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.
  1. For information objects whose purpose is to provide alternatives,

the set of tags associated with it should 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, a tag with multiple languages does not
   mean that one needs to be multi-lingual to get complete
   understanding of the document.
   Example: MIME multipart/alternative.

Alvestrand Best Current Practice [Page 6] RFC 3066 Tags for Identification of Languages January 2001

  1. 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.

2.5 Language-range

 Since the publication of RFC 1766, it has become apparent that there
 is a need to define a term for a set of languages whose tags all
 begin with the same sequence of subtags.
 The following definition of language-range is derived from HTTP/1.1
 [RFC 2616].
           language-range  = language-tag / "*"
 That is, a language-range has the same syntax as a language-tag, or
 is the single character "*".
 A language-range matches a language-tag if it exactly equals the tag,
 or if it exactly equals a prefix of the tag such that the first
 character following the prefix is "-".
 The special range "*" matches any tag.  A protocol which uses
 language ranges may specify additional rules about the semantics of
 "*"; for instance, HTTP/1.1 specifies that the range "*" matches only
 languages not matched by any other range within an "Accept-Language:"
 header.
 NOTE: This use of a prefix matching rule does not imply that language
 tags are assigned to languages in such a way that it is always true
 that if a user understands a language with a certain tag, then this
 user will also understand all languages with tags for which this tag
 is a prefix.  The prefix rule simply allows the use of prefix tags if
 this is the case.

3. IANA registration procedure for language tags

 The procedure given here MUST be used by anyone who wants to use a
 language tag not given an interpretation in chapter 2.2 of this
 document or previously registered with IANA.

Alvestrand Best Current Practice [Page 7] RFC 3066 Tags for Identification of Languages January 2001

 This procedure MAY also be used to register information with the IANA
 about a tag defined by this document, for instance if one wishes to
 make publicly available a reference to the definition for a language
 such as sgn-US (American Sign Language).
 Tags with a first subtag of "x" need not, and cannot, be registered.
 The process starts by filling out the registration form reproduced
 below.
  1. ———————————————————————
 LANGUAGE TAG REGISTRATION FORM
 Name of requester          :
 E-mail address of requester:
 Tag to be registered       :
 English name of language   :
 Native name of language (transcribed into ASCII):
 Reference to published description of the language (book or article):
 Any other relevant information:
  1. ———————————————————————
 The language form must be sent to <ietf-languages@iana.org> for a 2-
 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>.)
 When the two week period has passed, the language tag reviewer, who
 is appointed by the IETF Applications Area Director, either forwards
 the request to IANA@IANA.ORG, or rejects it because of significant
 objections raised on the list.  Note that the reviewer can raise
 objections on the list himself, if he 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 2-week
 comment period.

Alvestrand Best Current Practice [Page 8] RFC 3066 Tags for Identification of Languages January 2001

 Decisions made by the reviewer may be appealed to the IESG [RFC 2028]
 under the same rules as other IETF decisions [RFC 2026].  All
 registered 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 language tag reviewer decides whether to allow a new registrant
 to update a registration made by someone else; in the normal case,
 objections by the original registrant would carry extra weight in
 such a decision.
 There is no deletion of registrations; when some registered tag
 should not be used any more, for instance because a corresponding ISO
 639 code has been registered, the registration should be amended by
 adding a remark like "DEPRECATED: use <new code> instead" to the
 "other relevant information" section.
 Note: The purpose of the "published description" is intended as an
 aid to people trying to verify whether a language is registered, or
 what language a particular tag refers to.  In most cases, reference
 to an authoritative grammar or dictionary of the 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
 language tag reviewer decides what constitutes a "good enough"
 reference material.

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
 ranges 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.

5. Character set considerations

 Language tags may always be presented using 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.

Alvestrand Best Current Practice [Page 9] RFC 3066 Tags for Identification of Languages January 2001

 The issue of deciding upon the rendering of a character set based on
 the language tag is not addressed in this memo; however, it is
 thought impossible to make such a decision 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 may produce suboptimal output when a
 mixed Japanese-Chinese text is encountered)

6. Acknowledgements

 This document has benefited from many rounds of review and comments
 in various fora of the IETF and the Internet working groups.
 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.
 In alphabetical order:
 Glenn Adams, Tim Berners-Lee, Marc Blanchet, Nathaniel Borenstein,
 Eric Brunner, Sean M. Burke, John Clews, Jim Conklin, Peter
 Constable, John Cowan, Mark Crispin, Dave Crocker, Mark Davis, Martin
 Duerst, Michael Everson, Ned Freed, Tim Goodwin, Dirk-Willem van
 Gulik, Marion Gunn, Paul Hoffman, Olle Jarnefors, Kent Karlsson, John
 Klensin, Alain LaBonte, Chris Newman, Keith Moore, Masataka Ohta,
 Keld Jorn Simonsen, Otto Stolz, Rhys Weatherley, Misha Wolf, Francois
 Yergeau and many, many others.
 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, and has provided a great deal of input to this revision.

7. Author's Address

 Harald Tveit Alvestrand
 Cisco Systems
 Weidemanns vei 27
 7043 Trondheim
 NORWAY
 Phone: +47 73 50 33 52
 EMail: Harald@Alvestrand.no

Alvestrand Best Current Practice [Page 10] RFC 3066 Tags for Identification of Languages January 2001

8. References

 [ISO 639]   ISO 639:1988 (E/F) - Code for the representation of names
             of languages - The International Organization for
             Standardization, 1st edition, 1988-04-01 Prepared by
             ISO/TC 37 - Terminology (principles and coordination).
             Note that a new version (ISO 639-1:2000) is in
             preparation at the time of this writing.
 [ISO 639-2] ISO 639-2:1998 - Codes for the representation of names of
             languages -- Part 2: Alpha-3 code  - edition 1, 1998-11-
             01, 66 pages, prepared by a Joint Working Group of ISO
             TC46/SC4 and ISO TC37/SC2.
 [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 1327]  Kille, S., "Mapping between X.400 (1988) / ISO 10021 and
             RFC 822", RFC 1327, May 1992.
 [RFC 1521]  Borenstein, N., and N. Freed, "MIME Part One: Mechanisms
             for Specifying and Describing the Format of Internet
             Message Bodies", RFC 1521, September 1993.
 [RFC 2026]  Bradner, S., "The Internet Standards Process -- Revision
             3", BCP 9, RFC 2026, October 1996.
 [RFC 2028]  Hovey, R. and S. Bradner, "The Organizations Involved in
             the IETF Standards Process", BCP 11, RFC 2028, October
             1996.
 [RFC 2119]  Bradner, S."Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC 2234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
             Specifications: ABNF", RFC 2234, November 1997.
 [RFC 2616]  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.
 [RFC 2860]  Carpenter, B., Baker, F. and M. Roberts, "Memorandum of
             Understanding Concerning the Technical Work of the
             Internet Assigned Numbers Authority", RFC 2860, June
             2000.

Alvestrand Best Current Practice [Page 11] RFC 3066 Tags for Identification of Languages January 2001

Appendix A: Language Tag Reference Material

 The Library of Congress, maintainers of ISO 639-2, has made the list
 of languages registered available on the Internet.
 At the time of this writing, it can be found at
 http://www.loc.gov/standards/iso639-2/langhome.html
 The IANA registration forms for registered language codes can be
 found at http://www.iana.org/numbers.html under "languages".
 The ISO 3166 Maintenance Agency has published Web pages at
 http://www.din.de/gremien/nas/nabd/iso3166ma/

Appendix B: Changes from RFC 1766

  1. Email list address changed from ietf-types@uninett.no to ietf-

languages@iana.org

  1. Updated author's address
  1. Added language-range construct from HTTP/1.1
  1. Added use of ISO 639-2 language codes
  1. Added reference to Library of Congress lists of language codes
  1. Changed examples to use registered tags
  1. Added "Any other information" to registration form
  1. Added description of procedure for updating registrations
  1. Changed target category for document from standards track to BCP
  1. Moved the content-language header definition into another document
  1. Added numbers to the permitted characters in language tags

Alvestrand Best Current Practice [Page 12] RFC 3066 Tags for Identification of Languages January 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Alvestrand Best Current Practice [Page 13]

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