In #33136 @TerjeBr discovered a few weird "language codes", e.g.

These are a combination of language code + country code, thus a locale actually.

I don't think one should be able to select e.g. en_AU as a language code, that would be unexpected data. In this case one should simply select en (English) for a language, and e.g. compose it with a known country code to get a locale, or select a pre-defined locale from the list.

So ultimately this data would be replaced by the locale domain, e.g.

This means we lose some specific language name translations, but i tend to believe we should do it. (IMHO it's not worth to preserve Australian English somewhere when translating a locale, English (Australia) could be sufficient)