Overview#ISO 639 is a international Organization for Standardization (ISO) standard Language Codes — Part 1: Alpha-2 code, is the first part of the ISO 639 series of international standards for language codes.
Part 1 covers the registration of two-letter codes.
The use of the standard was encouraged by IETF Language-Tags, introduced in RFC 1766 in March 1995, and continued by RFC 3066 from January 2001 and RFC 4646 from September 2006. The current version is RFC 5646 from September 2009. Infoterm (International Information Center for Terminology) is the Registration Authority for ISO 639-1 codes.
New ISO 639-1 codes are not added if an ISO 639-2 code exists, so systems that use ISO 639-1 and 639-2 codes, with 639-1 codes preferred, do not have to change existing codes.
If an ISO 639-2 code that covers a group of languages is used, it might be overridden for some specific languages by a new ISO 639-1 code.