Just a comment about the flashcards, but it also applies to the program. When you ask for a translation of "They spent" (per esempio), it would help with good practice if the user knew whether you mean that they spent time or money (or something else). I know it is in the context of the current lesson, but the user's brain needs to learn to think "in context", and "they spent" as a standalone has no context.
It could just as well mean "Hanno speso" (they spent money) as it can mean "Hanno passato" (they spent time). I know that you supposedly haven't taught the verb Spendere as of yet, but it is out there and at least some of us have learned more verbs than you have presented at this point. I don't know how you would do it, but at least think about more ways to present challenges "in context".