(Suggestion) Specialized practices
In the lessons and reviews, there are many different types of questions (such as listening then typing it in, translating sentences, repeating phrases, etc). I thought that it might be nice to be able to practice just one of these at a time. For example, someone might want to focus on listening to a sentence then typing it in. They could check some box (or something like that) where they can do a customized practice that just gives them questions where they do this. This would help people focus on one particular area if they want to improve it.
I second this suggestion. Although, since some questions may be easier than others (multiple choice, for instance), the rewards might vary for these specialized sessions.