Codes for constructed languages
ISO 639-2 and ISO 639-5 also have the code art for other artificial languages. BCP 47 similarly has the subtag art, which together with the 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, or art-x-Latino-sine-flexione for Latino sine flexione).
The old SIL language identifiers (usually written in capitals) are officially obsolete and should no longer be used. They formed the basis of the ISO 639-3 language codes, but some SIL identifiers that had been retired before the establishment of ISO 639-3 were later assigned to different languages within ISO.
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.
List of codes 
|Interlingue (former Occidental)||ie||ile||ile||ie|
|Lingua Franca Nova||lfn||lfn|
- The old BCP 47 language tags i-enochian, i-klingon and art-lojban are old tags that were grandfathered in. The last two are also deprecated in preference to the later three-letter codes.
- The ISO 639-3 standard previously included the code eur for Europanto, which was retired on 2009-01-16, with the reason “Nonexistent”..
- ISO 639-3 used to have the code occ for Occidental. This was retired on 18 July 2007, because Occidental is just another name for Interlingue, which has the code ile.
- The Wikipedia articles on Kotava and Romanova have been deleted as non-notable. Please see the external links.
See also 
- List of ISO 639-1 and ISO 639-2 codes on the website of the ISO 639-2 Registration Authority
- ISO 639 code tables on the website of the ISO 639-3 Registration Authority
- IANA Language Subtag Registry for IETF's language tags defined in BCP 47
- List of constructed languages on The Linguist List