ISO 639 (EN) Codes for the representation of names of languages
ISO 639 is a set of standards by the ISO that is concerned with representation of names for languages and language groups.
It was also the name of the original standard, approved in 1967 (as ISO 639/ and it was withdrawn in 2002. The ISO 639 set consists of five following parts.
ISO 639-1:2002 (EN)
Part 1: Alpha-2 code
ISO 639-1 provides two language codes, one as a two-letter code (ISO 639-1) and another as a three-letter code (ISO 639-2) for the representation of names of certain languages. ISO 639-1 was devised primarily for use in terminology, lexicography and linguistics. ISO 639-2 represents all languages contained in ISO 639-1 and in revision any other language, as well as language groups, as they may be coded for special purposes when more specifically in coding is required. The languages listed in ISO 639-1 are subset of the languages listed in ISO 639-2 each language code element in the two-letter code has a corresponding language code element in the three-letter code, but not necessarily vice versa. Both language codes are to be considered as open listing. The codes were devised for use in terminology, lexicography, information and documentation and linguistics. ISO 639-1 also includes guidelines for the creation of language code elements and their use in many applications.
ISO 639-2:1998 (EN): Alpha-2 code
ISO 639-2:1998 provides two sets of three-letter alphabetic codes for the representation of names of languages, one for terminology applications and the other for bibliographic applications. The code sets are the same except for twenty-five languages that have different language codes because of the criteria used for formulating them. The language codes were devised originally for use by libraries, information services, and publishers to indicate language in the exchange of information, especially in computerized system. These codes have been commonly used in the library communities and may be adopted for any application requiring the expression of language in coded form by terminologists and lexicographers. The alpha-2 code set was devised for practical use for most of the major languages of the world that are most frequently represented in the total body of the world’s literature. Additional language codes are created when it becomes apparent that a significant body of literature in a particular language exists. Languages designed exclusively for machinery use, such as computer programming languages, are not included in this code.
ISO 639-3:2007 (EN) Part 3: Alpha-3 code for comprehensive coverage of languages
ISO 639-3:2007 (EN) shares a code, published by the Registration Authority of ISO 639-3, consisting of language code elements comprising three-letter language identifiers for the representation of languages. The language identifiers according to this part of ISO 639 were devised for use in a wide range of applications, especially in computerized systems, where there is potential requirement to support a large number of the languages that are known to have ever existed, whereas ISO 639-1 and ISO 639-2 intended to focus on the major languages of the world that are most frequently represented in the total body of the world’s literature, ISO 639-3 provides as complete an enumeration of languages as possible, including living, extinct, ancient and constructed languages, whether major or minor, written or unwritten. As a result, ISO 639-3 deals with a very large number of lesser-known languages. Languages designed exclusively for machine use, such as computer-programming languages and reconstructed languages, are not included in this code.

ISO 639-4:2010 (EN) Implementation guidelines and general principles for language coding
ISO 639-4:2010 shares the general principles of language coding using the codes that are specified in the other parts of ISO 639 and their combination with other codes. Furthermore, ISO 639-4:2010 provides guidelines for the use of any combination of the parts of ISO 639
The terminology and general descriptions of ISO 639-4 are intended to replace corresponding text of other parts of ISO 639 as relevant in future revisions. Relevant metadata for the description of linguistic entities are also shared, as a framework for databases of linguistic data to support the ISO 639 series

ISO 639-5:2008 (EN) Alpha-3 code for language families and groups
ISO 639-5:2008 (EN) provides a code consisting of language code elements comprising three-letter language identifiers for the representation of names of living and extinct language families and groups. Languages designed exclusively for machine use, such as computer-programming languages, are not included in this code.
ISO 639 shares codes for the identification of languages, language variations, and language groups. The identifiers may be used to denote the language used in a text, the language of terms or words in a dictionary or terminological database, the language used in a spoken presentation, language capabilities of software, etc.
ISO 639-2 includes some language groups and language families, but by not a complete list. The purpose of the code elements for language groups and language families in ISO 639-2 is to provide a meaning to register the language of a document even when the individual language in question is not included in the code table. ISO 639-5:2008 supplements the coding of language groups and language families in ISO 639-2. However, the detailing of coding in ISO 639-5:2008 is intended to support the overall language coding of the ISO 639 series of International Standards rather than provide a scientific classification of the languages worldwide.
The list of language families and groups in ISO 639-5 will be extended and developed continuously through a defined maintenance process.
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