Function that returns the list of Language Codes

I think we should also update the documentation of the above functions. They can take a "kde locale" (I don't know if we have a standard name for that) such as ca@valencia, which is not a iso 639-1 code as mentioned. If that code is not found it falls back to Qt QLocale function (and iso code).

How should it be called? Kde locale? Kde language code?