Lesson structure for new vocabulary
This is a small but frustrating issue I've noticed that seems to be caused by the seemingly random order of the questions in each lesson. On some (but not all) questions, words are underlined, indicating that you can click on them to find out their translation. However, sometimes a word will be introduced as part of a question without the option to do this, and as the user has not yet learnt what that word means, you either have to consult a dictionary online (which surely defeats the purpose of the app) or just fail the answer.
For example, I was doing a German lesson the other day and it introduced the word for 'gate' by showing me a picture of a gate and asking for the translation. As I had never encountered this word in Duolingo before I had no chance to pass the question successfully, which seems a bit unfair.
The obvious solution to this problem is to simply only allow words to be introduced as part of a question where the user can see what the word means in both languages, and only after this has happened at least once, then allow it to be used as part of the harder questions where a translation is not provided as an option.