LoC hosts the Website of the ISO 639 Joint Advisory Committee (ISO 639/RAs-JAC) of the two Registration Authorities for ISO 639-1:2002 and 639-2:1998. Below you can find useful information that helps you understand more about the ISO language codes.
In 2004, the two RAs appointed as secretary of the Joint Advisory Committee (ISO 639/RAs-JAC) Mr. Håvard Hjulstad, who maintains the register of language identifiers and processes requests for additions to the list of language identifiers. He also maintains an accurate list of information associated with registered language identifiers and updates of registered language codes: ISO 639 Code list (Library of Congress).
Some languages have both two-letter and three-letter identifiers, and a few have two different three-letter identifiers. Some languages are listed in Part 3 only, while other languages are listed in Parts 1, 2 and 3. This is the result of the historical development of the standard, and it does not reflect “status” or “importance” of a language.