Substitute a word requires certain language knowledge. This should be tested somehow, so that the application knows the user level. For example, having no prior Spanish knowledge I would not do substitute a word, and i can do listen exercises which show me some common words and already teach me something. This was enjoyable... for the first 3 minutes.

After just one run and 3 minutes into the registration it already is asking for money? I have no problem paying when I see what I'm paying for. Here I had too little time to see, and already am annoyed by this. So cloze-listening is already unreachable for me, and I would not play the other game without having any language knowledge. Fail right here.

Learning a language is a task for months, you'll (the author) be very safe asking for money after several days or even weeks of trial.