They just announced that they are releasing new languages.
In addition to Spanish, French, Portuguese, Italian, German, Irish, Swedish, Dutch, and Danish, you can now learn:
There was a ThinkGeek April Fools joke that advertised Rosetta Stone’s Klingon, but it looks like DuoLingo is doing this for real.
I also came across this video of a kid who learned to speak English in eight months using DuoLingo (in addition to Skyping with native speakers and chatting on WhatsApp).
And to think I was proud of myself for being able to properly order dinner in Russian after years of study.
See 3:14 into the video.