Idiomatic expressions in French
It's in the discussions before and it's really a serious problem: The material in the French part is made without awareness of the relationship between the language and the sentences. The sentence "C'est l'arbre qui cache la forêt." is to be translated to "You cannot see the wood for the trees." this is but one of many examples of this problem that occurs in the French course. The point I am trying to make is that it is not possible to translate this sentence using the knowledge that has been taught up to the point . Duolingo is unnecessarily making the student feel stupid. Instead of successively building up our language ability and using that ability we are forced to memorize sentences to progress in the system. In other words, the course should introduce new elements bit by bit and use examples that can be handled using what has been learnt. So please, Duolingo, go through the French material and remove the idiomatic expressions. There was an easy way to avoid this problem. It doesn't occur in the Spanish course. So much of the Spanish material could have been produced by translating the Spanish (the grammar is rather similar).
I really hate Idioms. Sometimes Duo doesn't let you know that is an Idiom even when you highlight it, so you have to learn from the discussion button. They also don't really show up in practice enough, so they are easy to forget and when they show up again I make the same mistakes.
Idioms are one of the most annoying things about any language, English has lots too so they must be annoying for English learners. They are an important part of learning a language though. I don't think they should be removed. I think there should perhaps be a section devoted to Idioms near the end of the tree. Idioms could put off a learner if they introduced too early.