I think the best thing is for Wine to support things like LC_ALL="nn nb" LANG="nn nb" because even though we provide a Nynorsk translation, most programs will only be available in Bokmål.
It seems that Vista supports many user preferred languages and many system fallback languages so it should possible to implement. But I don't know how it works "under the hood". Are the functions from ntdll documented somewhere?
I've put Chinese and Portugese on the Wiki as languages using sublang codes because we already have distinct translations for different variants using the sublang codes. Also as far as I know the variants are quite different and in other open source projects they also usually have distinct translations. But of course it would be interesting to learn what native speakers think about it.
Mikolaj Zalewski