Which language codes are supported by Launchpad?

Launchpad uses ISO-639 language codes: two-letter ISO-639-1 codes where available (http://www.sil.org/iso639-3/codes.asp?order=639_1) and three-letter ISO-639-3 codes for other languages (http://www.sil.org/iso639-3/codes.asp?order=639_3).

Please be aware of the following guidelines:
- Do not append a specific country code, especially not if it is the language's home country (NOT fr_FR, es_ES, de_DE but also avoid fr_BE, es_AR, de_AT etc.).
- Some language codes are for language groups rather than a specific language. Don't use those either.
- There are some exceptions where they are needed: pt_BR, zh_CN, and zh_TW.
- More exceptions for special cases can be made on a per-project basis but please try without them first.
- Source strings are always in U.S. English, therefore translations to English (en and en_US) are not supported at all.

You can also query the Launchpad language database here:
https://translations.launchpad.net/+languages
You can either enter a language code or a language name. Go to the page for the specific language by clicking on that language's name and look for "Active in Launchpad" in the box on the right to see if it can be used.