ISO 639-6

ISO 639-6 was an international standard that attempted to provide a comprehensive list of language codes, covering even languages with very few speakers or that are now extinct. It was intended to be a more detailed and expansive alternative to other parts of the ISO 639 standard family, particularly ISO 639-3. ISO 639-6 language codes were four-letter identifiers.

The Registration Authority for ISO 639-6 was the Center for Information as Language (CILA).

While its goal was laudable, ISO 639-6 faced significant criticism for several reasons. The methodology used to identify and classify languages was opaque and not always well-documented. Its inclusion of many poorly attested or constructed languages, often based on genealogical hypotheses rather than demonstrable linguistic features, led to accusations of inflating the number of recognized languages. There were also concerns about the data quality and the maintenance of the standard.

Due to these criticisms and practical issues surrounding its implementation and maintenance, ISO 639-6 was officially withdrawn on November 25, 2014. The ISO 639-6 standard is no longer actively maintained or recommended for use. Other parts of the ISO 639 standard family, such as ISO 639-3, are preferred for language identification. Existing implementations that relied on ISO 639-6 codes are encouraged to migrate to other standards.