Wow, that's really sloppy on Firaxis' part. I've been annoyed by the inconsistency in their localization techniques before, but obviously English is much more forgiving.
This would be quite an undertaking. Unfortunately, the CvLocalization library is not part of the released source code. The nominative/accusative routine would be doable (though certainly not trivial) with a Lua string parser, especially since we already have the database of gender/plurality (even if Firaxis ignores it half the time), but you'd still have to make a lot of changes to a lot of Lua files.