An idea for idioms.
I think Duolingo should identify words or sentences as idioms when they appear. I am trying to learn French and this has been very challenging for me. It is only made worse when I run into an idiom (without knowing it) and I have to apply my very rudimentary skill set (which idioms, a lot of the time, don't follow) to attempt to solve the French puzzle before me. Then, when I do get it wrong, there still is no disclosure informing me that it is an idiom. This could potentially confuse a lot of new Duolingo users who may not know the useful nature of the community tab. Thanks for your consideration.
In fact, they are working on improving the experience with idioms. In German, some phrases have already received combined hover hints that reveal the whole idiom. I'm sure that with time all the languages will be polished, but, unfortunately, we have to wait because the team is quite small and the work is big. I'm also sure the lessons that we have now are much better than those of a year ago.