Thanks for the helpful feedback!
I think I can get the listening-only or reading-only modes ready very soon, as those are easy to implement with my current code base. Reverse mode could definitely be good, I’ll have to best think of the implementation since it would require 1,000 English voice clips which is easy to generate and my code would have to be modified in a couple places.
Can definitely tweak the other two aspects. By leveling up, do you mean how quickly a word is mastered, or how often new words are added to the bank?