This is a list of ISO 639 codes and IETF language tags (BCP 47) for individual constructed languages, complete as of January 2023[update].
[1] The BCP 47 subtag x can be used to create a suitable private use tag for any constructed language that has not been assigned an official language tag (e.g., art-x-solresol could be used for Solresol).
The old SIL language identifiers (usually written in capitals) are officially obsolete and should no longer be used.
The IANA Language Subtag Registry (for IETF’s language tags defined in BCP 47) was updated on 29 July 2009 to include all ISO 639-3 and ISO 639-5 identifiers in use at that time.
When a constructed language has multiple writing systems, the following BCP 47 tags can be used to differentiate between them.