Translating Duolingo itself to other languages
A friend of mine only knows some english but wants to get better, but for the time being, you can only learn english if you already know spanish. I would gladly help to translate duolingo into my mother tongue (swedish), but at the moment I can't.
I think it would be a good idea to let users proficient in a language translate the duolingo website itself to that language, so that not only english or spanish speaking people can learn new languages.
The ability for users to add new languages is coming down the pipe (or so I've read), so with any luck you'll be able to do this sometime in the not-too-distant future.
Looking forward to learning Swedish!