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.
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.