get_language_from_abbr() does not recognize ui_language

[DanielNoord]

When using get_language_from_abbr() to get the full string of the ui_language in user_data None will be returned. This is because the ui_language is not added the languages lists that get_language_from_abbr() uses. I think this would be solved by making the lookup from get_language_from_abbr and get_abbreviation_of be based on a stored list of language-abbreviation pairs.

Besides, I think returning None when failing to find the abbreviation is not really expected behavior and it would be better if an exception was raised. Raising that exception should be easy and I can make a PR if you want.