Suggestion: Icon for Completed Tree
I know there have many requests for some sort of visual indication on your profile that you have completed a tree. There are many reasons for this, but I think it's a crucial thing to have. I have a suggestion that would be easy to implement and would not change the current profile or language icon structure.
Learners get feedback from the duolingo community; someone that is level 13 in a given language may be a beginner partway through the tree (like me in German) or could be someone who tested out of all or part of the tree due to outside knowledge of the language. Knowing which is the case can be important when getting answers to questions, particularly if they differ. As well, it would be very satisfying and fulfilling to have a lasting mark of completion; currently, the only indication after you've closed the pop-up message is the golden owl you see at the bottom of your tree. There is nothing on your profile, which I know I found a little disappointing, and no one else has any indication you're done. I am very grateful to AlexisLinguist for the golden owl hall of fame thread she has put together.
My suggestion - outline the flag icon in gold. This could be done both on the profile where there is detailed information about progress in each language and in the small icons next to people's names in discussions, and it would scale, where a trophy icon may not allow someone to easily tell what language it represents. It only requires having some sort of tag that all skills are completed, which must be available somewhere because of the golden owl at the bottom of the skill tree.
I do also want to say thank you for all that you have done with duolingo so far - I've loved everything and look forward to learning more and more!
Sounds like an easy and simple solution to implement. Hope that Duolingo staff see this! I think that this is a great idea. A little recognition never hurt anybody. Have some lingots for your awesome idea! =)