ISO 639-2: Three-letter codes for languages

Structure and code types

Each entry in ISO 639-2 is a three-letter lowercase code. The standard includes entries for individual languages, macrolanguages or collections, and several special-purpose codes used to indicate undetermined or multiple languages. For a subset of languages there are two distinct three-letter codes: a bibliographic code (B) and a terminologic code (T). The B/T distinction exists for historical and bibliographic reasons and both codes are recognized by the standard.

Examples and special codes

• Common language examples: eng (English), spa (Spanish), fra or fre (French), deu or ger (German), chi or zho (Chinese).
• Special-use codes: und (undetermined), mul (multiple languages), zxx (no linguistic content).

History and maintenance

ISO 639-2 was introduced as an extension of earlier parts of ISO 639 to cover many more named languages than two-letter codes allowed. It is used alongside other parts of the ISO 639 series: the shorter ISO 639-1 two-letter codes for major languages; ISO 639-3, which attempts a comprehensive inventory of individual languages; and ISO 639-5, which deals with language families and groups. National libraries and standards bodies participate in the maintenance and updates of the lists; bibliographic communities historically influenced some legacy code choices.

Uses and importance

ISO 639-2 codes are widely used in library catalogs, bibliographic records, archival descriptions, digital repositories, and technical standards that require language tagging. They provide interoperability for exchanging metadata between systems and are commonly found in cataloging rules, content management systems, and language-tagging mechanisms in software and data formats.

Distinctions and notable facts

• Coexistence with two-letter codes: many languages have both ISO 639-1 (two-letter) and ISO 639-2 (three-letter) identifiers; software often accepts either form depending on context.
• Bibliographic vs terminologic codes: where both exist, B codes reflect traditional library usage while T codes align more closely with modern linguistic names; both are valid for interoperability.
• Relationship to other parts of ISO 639: ISO 639-2 focuses on widespread bibliographic needs, while ISO 639-3 expands coverage to smaller or more narrowly defined languages and ISO 639-5 classifies groupings.

For authoritative lists, code status, and updates consult the published register for the ISO 639 family or national and international bibliographic authorities; see the broader ISO 639 family for context and references to related parts of the standard.