The app walks a weird tightrope. On the one hand, it has to teach language, otherwise we won't use it. On the other, it has to encourage you to do microtransactions or pay for premium, and it does this by making the interface annoying and buggy until you pay (but not annoying enough to make you delete it). At the very least, if you fail a test because of a bug or intentional UI glitch, it should refund your gems. Makes it feel like you can never do well no matter how correct your answers are.