Study Quest has very little content in its own right for basic language learning of any language aside from Japanese. Well, that shouldn't really be a problem since players can add in their own flash cards to help remember Spanish words and expressions, right?
No! It costs money for players to make content for the game's developers as each item you input into this app similar to Anki, an open-source Linux application which doesn't charge you to use it, it costs you an “oin” which costs about 1¥ or cent each, which I know is a very low cost and all, but you are still charging people for crowdsourced content creation which I consider to be a donation.
Oh, and the real reason I rated this app 1 Star is because I wasn't having fun battling monsters or learning any Spanish words. Personally, I found the Match-3 battle mechanic distracting or annoying rather than holding my focus.