Recently I noticed that Duolingo now offers to tweet/post to Facebook about finished levels (ie., food, animals, whatever). When clicking on the "Tweet"-Button, I'm only forwarded to Twitter, with "http://www.duolingo.com" offered as text for my tweet. I think there could be more here: Some kind of picture/link sharing (maybe just forward to the users profile, or some database extract regarding the learned skill like "[User] has learned [skill] on [date]"?), so it kind of certificates that the user actually did something and not just fakes it (which might be the case if I just tweet "Did this and that"). If forwarding to the profile, you could add explanations for the language levels – future employers might be interested in this ;-) (besides, I think people who tweet/post about such stuff are hotter than those posting about heir FarmCandycrushwhatnot)
[Further edited:] See, that's what I want to tweet about: http://imgur.com/q0HCiqA
Any opinions on this?