In biblio records, language is edited using LANG authorized values, so we should also use it in advanced search filter. This will make is way easier to manage possible languages.
Somehow depends on Bug 25376
LANG is not used in MARC21 by default at the moment and I think these are separate use cases. You can assume that your catalogers will all catalog in one language, but you can't assume the same for your OPAC users. I think we need to replace the database approach we currently have as bug 12017 suggests, but using the authorised value list is not the right approach, because it will require individual work by each library for a standardized list and is untranslatable. Personally I have translated languages multiple times now (once for the list XSLT uses, which is a great feature) and would be more than happy to have those reused instead of having to do it again for SQL :)
I'm not working on patches for this
(In reply to Fridolin Somers from comment #3) > I'm not working on patches for this