chatting on duolingo classrooms
It would be more easy to communicate with students if duolingo has a chatting system in classrooms where we could convey concepts better.
I think Duolingo is trying to stay focussed on its core task. Creating chat rooms would mean they would have to do a lot more monitoring and moderating.
There's nothing to stop you using a chat system with your students, though. Your school's VLE is probably the best place to do so.