These codes are a useful international and formal shorthand for indicating languages.
(Two-letter country-specific top-level-domain code suffixes are often different from these language-tag prefixes.)
ISO 639, the original standard for language codes, was approved in 1967.
It was split into parts, and in 2002 ISO 639-1 became the new revision of the original standard.
Infoterm (International Information Center for Terminology) is the registration authority for ISO 639-1 codes.