Greek and Latin?
When would Duolingo teach us Greek and Latin? They may be languages used by few people, but they're really things that help us understand more about culture.
Duolingo is not going to add any more languages but they will work to make it possible for the users to add new languages. This is not coming very soon.
You won't be able to learn them on Duolingo, but if you want to refresh your Latin, try the Latinum podcast. It's Latin lessons, starting from the very basics, read to you. There are grammar discussions and Latin and English sentences that you're supposed to translate. I think it's awesome.