Tags for Identifying Languages
RFC 5646

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Network Working Group                                   A. Phillips, Ed.
Request for Comments: 5646                                        Lab126
BCP: 47                                                    M. Davis, Ed.
Obsoletes: 4646                                                   Google
Category: Best Current Practice                           September 2009

                     Tags for Identifying Languages

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.

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.

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Phillips & Davis         Best Current Practice                  [Page 1]
RFC 5646                     Language Tags                September 2009

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Language Tag . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . .  4
       2.1.1.  Formatting of Language Tags  . . . . . . . . . . . . .  6
     2.2.  Language Subtag Sources and Interpretation . . . . . . . .  8
       2.2.1.  Primary Language Subtag . . . . . . . . . . . . . . . . 9
       2.2.2.  Extended Language Subtags  . . . . . . . . . . . . . . 11
       2.2.3.  Script Subtag  . . . . . . . . . . . . . . . . . . . . 12
       2.2.4.  Region Subtag  . . . . . . . . . . . . . . . . . . . . 13
       2.2.5.  Variant Subtags  . . . . . . . . . . . . . . . . . . . 15
       2.2.6.  Extension Subtags  . . . . . . . . . . . . . . . . . . 16
       2.2.7.  Private Use Subtags  . . . . . . . . . . . . . . . . . 18
       2.2.8.  Grandfathered and Redundant Registrations  . . . . . . 18
       2.2.9.  Classes of Conformance . . . . . . . . . . . . . . . . 19
   3.  Registry Format and Maintenance  . . . . . . . . . . . . . . . 21
     3.1.  Format of the IANA Language Subtag Registry  . . . . . . . 21
       3.1.1.  File Format  . . . . . . . . . . . . . . . . . . . . . 21
       3.1.2.  Record and Field Definitions . . . . . . . . . . . . . 23
       3.1.3.  Type Field . . . . . . . . . . . . . . . . . . . . . . 26
       3.1.4.  Subtag and Tag Fields  . . . . . . . . . . . . . . . . 26
       3.1.5.  Description Field  . . . . . . . . . . . . . . . . . . 26
       3.1.6.  Deprecated Field . . . . . . . . . . . . . . . . . . . 28
       3.1.7.  Preferred-Value Field  . . . . . . . . . . . . . . . . 28
       3.1.8.  Prefix Field . . . . . . . . . . . . . . . . . . . . . 31
       3.1.9.  Suppress-Script Field  . . . . . . . . . . . . . . . . 32
       3.1.10. Macrolanguage Field  . . . . . . . . . . . . . . . . . 32
       3.1.11. Scope Field  . . . . . . . . . . . . . . . . . . . . . 33
       3.1.12. Comments Field . . . . . . . . . . . . . . . . . . . . 34
     3.2.  Language Subtag Reviewer . . . . . . . . . . . . . . . . . 35
     3.3.  Maintenance of the Registry  . . . . . . . . . . . . . . . 35
     3.4.  Stability of IANA Registry Entries . . . . . . . . . . . . 36
     3.5.  Registration Procedure for Subtags . . . . . . . . . . . . 41
     3.6.  Possibilities for Registration . . . . . . . . . . . . . . 46
     3.7.  Extensions and the Extensions Registry . . . . . . . . . . 49
     3.8.  Update of the Language Subtag Registry . . . . . . . . . . 52
     3.9.  Applicability of the Subtag Registry . . . . . . . . . . . 52
   4.  Formation and Processing of Language Tags  . . . . . . . . . . 53