Create a button which is useful to organize the words by their taughtedness. (Red-Green)
Create a button which is able to organize the visible word count on a certain page with detailed, choosable options-like 10-20-50-100.
Create a button which is capable to organize the words by their word-class.
Give availability to print them.
Extend the whole topic with more advanced grammar. It is actually way too scarce in quantity and quality.
Give more detailed descriptions about certain rules.
Give more examples.
Fill the missing pronunciations.
Make a button which is for increasing the window size.
Give an option to eliminate the unwanted course.
Improve the courses with more words.
I would say that some kind of speaking exercise would be vital as well, but from what i've seen, even the French is hardly a half made course.
Furthermore, in the other languages, there isn't any listening or reading option.(At least the most of i've tried).
I can't emphasize enough that most of the content is not in a complete form.
So, even if you upgraded the necessary features, it still would be nice.