Suggestion: List of new vocab words for all lessons.
I think it would be a good idea for each topic to have a new thumbnail indicating a list of new vocabulary words (with or without the translation of all lessons). It would allow more advance people to see if they know all the vocab and allow them to skip the lesson without having to do all lessons to make sure they know everything.
Not really an answer here, but I totally agree with you! This would be a very good addition!
if you click on the skill you want to learn and then on the lock in the topright corner you can take a test to pass all lessons in the skill.
But that's not the point. The point is to know the new vocab before you try the test.
For example, I am a Intermediate German speaker, but because the process of Duolingo is kinda slow, I cannot see if there is new vocab in the lessons I do, and because I don't want to miss anything, I do all lessons even if there may be only one word I don't know.
I am also more experienced at the language I am learning now, but I figure I'll stumble acros the words I still don't know. And then I'll learn them. A lot of the words are repeated in later lessons. Don't worry.