ISO 639-6

ISO 639-6, Codes for the representation of names of languages — Part 6: Alpha-4 code for comprehensive coverage of language variants, is an international standard in the ISO 639 series, developed by ISO/TC 37/SC 2 (International Organization for Standardization, Technical Committee 37, Subcommittee 2: Terminographical and lexicographical working methods). It contains four-letter codes that denote variants of languages. This allows to differentiate between, for example, historical versus revived  Manx, while ISO 639-3 only includes   for Manx.

The data supporting ISO 639-6 is being researched and compiled by GeoLang on behalf of the British Standards Institution (BSI). ISO 693-6 was published in 2009. The database also links each language to its principal ancestor allowing the user to follow the develoment of various languages. For example, the codes and ancestry of English is given below:

The database differentiates between different scripts used for the same language. For example, a number of different scripts were used in the Ottoman Empire and as a result the Ottoman Turkish language has been categorised as follows: