About the lessons on idioms (German).
I looked around, and while there are discussions about this already, many of them are quite old.
So, I kind of just got started, after some time of not taking any German lessons and found duolingo very useful in keeping me practising and from forgetting. That is, until I got to the Idioms lessons.
They don't always admit literal translations, so most of the time I found myself trying to guess with which particular English phrase they could be "substituted", making the lesson very frustrating. One of them didn't even admit the modern spelling form "pigeon" and kept correcting it to the alternate "pidgeon" (which even both my browser and text processor mark as incorrect), a much more archaic form.
I'm just suggesting here that maybe idioms should be kept literal and having them explained instead of proposing equivalent phrases in a way that actually clashes with the way vocabulary and syntax are managed and presented in the lessons.