Duolingo has helped me so much in Spanish, but they should also teach AMERICAN SIGN LANGUAGE!!! That would be awesome and because it's universal, so VERY helpful. Rate up if you agree!
I'm not a programmer, but i can't see how it would work very well, unfortunately (at least on this site). You'd have to see the signs in action, which means video, which means pre-recorded sentences. And signs change meaning depending on the facial expression along with it. Duolingo has some kind of algorithm in place that creates new random sentences out of the words you know every time you practice, but I can't see how that would work with video.
@elae Yes there are different regional versions of sign language. Wikipedia has a good map. ASL is perhaps the most widely spread but is by no means universal. That being said, I would love to be able to learn it through Duolingo if they could work out the logistics of measuring it!
Sign languages are not universal. The one that is most frequently used in North America is American Sign Language, but there is French Sign Language, Japanese Sign Language, German Sign Language, Quebec Sign Language, and British Sign Language (which is extremely different from ASL) just to name a few from the top of my head which are all separate languages. Here is a link just to give you an idea of the number of sign languages there are: http://en.wikipedia.org/wiki/List_of_sign_languages
Signed languages form just as spoken languages do, at differing times between different groups in vastly different ways. For instance, ASL came out of a combination of a sign language between the Deaf of Paris along with sign languages from Native Americans and from a population on Maratha's Vineyard that had a genetic predisposition for deafness, causing them to formed their own sign. Meanwhile Italian Sign is so vastly different from spoken Italian that its sentence structures and other linguistic components are closer to Cree and Sanskrit despite a lack of a historical link between the three languages.