Comment 3 for bug 16

How about this?

If you have both language "Language-foo" and "Language-foo (Region-bar)", merge all translations made for "Language-foo" into "Language-foo (Region-bar)" and remove "Language-foo" entirely. When there are conflicts, use the translation from "Language-foo (Region-bar)". For languages with several regions, choose arbitrarily. Often it's obvious ("Swedish" should be "Swedish (Sweden)" rather than "Swedish (Finland)"), and if it isn't e-mail a random translator of one of the involved languages and ask (or simply make something up).

Then, only languages with no region specification available (I'd guess Esperanto & friends) retains their regionless name.

This scheme would fall over if there's a language that both exists as a general language and with a region specification, and there's a noticable difference between the general version of the language and the language spoken in a certain region. Whether or not that's the case I have no idea, but it should at least be a lot less common than the current "Swedish" vs "Swedish (Sweden)" problem.