That's pretty cool, I've never heard of Duolingo either but it sounds like a fantastic tool to learn languages.
Personally I can't learn a 2nd language, I've tried a couple (Japanese for 5 years + Italian casually) and just can't. It's weird, I can learn to read and speak other languages... But I can't comprehend what it means. If I could Klingon would be near the top of the list, as a casual fan it'd be fun.