Please add some way for us to distinguish people who finished learning a language. Something like different color of number indicating language level or some other mark next to the language flag.
I am suggesting this because someone who already studied the language or a native can go through a skill tree very fast and in the end acquire less points and level than a person studying the same language from scratch. For instance I'm lvl 16 in Italian while some people that have completed Italian have lower levels.
I like this idea. It would give an instant "feel" for the person's ability. Of course, one can never stop learning a language and the end of the tree is really just a way-point. I know I still have masses to learn even though I have finished the tree. I agree also that it would be useful to see what languages people consider themselves to be fluent in.
At the moment it is only possible to check out a user's skill tree, but even this may misrepresent a person's level for a number of reasons. They may be just so good at a particular language that it disinterests them to do it, or they may be just starting on duolingo then you see a few weeks later they have finished the tree.
I also feel that some mark of distinction would be a goal to aspire to. I have been learning Italian a few years now but it was a huge challenge for me to complete the tree. I even got my wife in to watch as I completed the last question thinking something nice, or funny or whatever might happen. But NOTHING!!! For all that work!! Not even a hoot from the duolingo owl :(
I agree that finishing the tree does not really show the real level one has... I mean, I finished the English tree in few hours on one evening, taking all the shortcuts, and I know my English is faaar from perfect. On the other hand, I am a native Spanish speaker and I just removed Spanish from my list (I did not take Spanish, but someone asked me if I could help in a translation and I got points) and had level 5 Spanish, so it does not really show the real skills one has.
I think someone suggested indicating the native language somehow, too, but I disagree that being a native shows you have a good level for people to learn from you. I know this is a public tool and all, but if you write awfully in your own language, it is unlikely that you can help people that is starting with it. Or maybe you write alright, but do not know the rules; I may know something is correct, but not why (it has happened to me few times already, so I did not answer or could not answer something completely). So I think in the end it does not really matter that much that someone gets a different colour or a mark.
I also expected some sort of celebration when I completed the tree, by the way :__D
Perhaps a little star that shows up on the flag of the language? Or something that shows up alongside the 'streak' icon. I like this idea as well, but it would hardly represent fluency unfortunately... I have some friends who I KNOW could not possibly be even close to proficient in the lessons that they have done so far, yet their skill tree says they've completed these lessons. I like this idea purely for the fact of completing the skill tree.