properly do language fallback again

i think at some point in the refactorings, this broke. without this i get no language fallback but empty documents in the request language if the request language does not exist.

btw, why does the !$fallback case just before this case still try to fallback to the default locale? does that make sense? i think it should only do that if $locale was empty but not if the locale was not empty and translation loading failed.