I would consider this pretty challenging, even though I don't make add-ons.
Here's an idea. An in-game translator. Not a common to orcish or orcish to common. Nothing like that. More like an accusal translator. For an example, English to Russian. The message could be translated almost instanly with a hotkey of some sort. I'm not sure, but this may not even be possible. You would need to be an absolute master at atleast two languages. This would take alot of time because you would need to find every translation for every word(might be out on the internet some where).
Me? Too lazy to learn a language... I tried rossetta stone... Got bored.