Speaking as a native English speaker from London: I can assure you that most Brits would get this question wrong. It is true that Brits use "jolly" to mean "very" but it is, as you've noted, informal. Brits do not use it this way in formal speech. You would have to make it clear in the question that you were talking about informal English. E.G. "Name a word that means 'happy' and can also informally mean 'very'".

@Tomek_zemla: The people in this thread are trying to help you. We are taking the time to tell you about our experience using your app. Feedback is a gift. Be grateful for it. Do not get defensive. If somebody tells you that they found your app baffling and difficult, then you are not going to change their mind by arguing with them. Instead, you should think about how you can change your app so that people find it useful and fun. You have the germ of a good idea for an app here. It needs more work before it's viable. We are trying to help you identify what you need to do to make it good.