This looks neat. If you’re going to add Duolingo style features, please don’t add fill-in-the-blank or word matching to the question types; or at least make them optional. They are an incredibly frustrating waste of time on Duolingo—they take up a ton of time to solve and don’t actually improve comprehension. My biggest gripe with Duolingo is that half of the questions asked in a lesson are questions like these which have the pretense of helping you learn but don’t actually deliver. I think if you instead came up with some very difficult question types that really challenged someone’s comprehension, it would be stickier than Duolingo (especially for the HN crowd who is actually trying to learn) and not just here to “play a game” like a large portion of the Duolingo audience.