scope:

This part of ISO 639 provides four-letter representations (alpha-4) and language identifiers
for language variants and a framework for relating them to languages, language families, and
language groups. The alpha-4 representations have been developed for use in a wide range
of applications, especially in computer systems, where there is a potential need to cover the
entire range of languages, language families and languages as well as language variants
within each identified language. Alpha-4 representations will support the quantity of known
language variants and accommodate any future expansion.
This part of ISO 639 provides a hierarchical framework, which facilitates backward
compatibility with other ISO 639 codes, based on linguistic and/or geo-linguistic relationships,
within which a comprehensive enumeration of language variants is possible, including living,
extinct, ancient and constructed languages, whether major or minor. As a result, this part of
ISO 639 caters for a very large number of languages and their variants. Registrations for
languages designed exclusively for machine use, such as computer-programming languages
and reconstructed languages will not be included in this standard.