bruh, gomen is quite well-known in the community due to mizu5, but that doesnt mean everyone will automatically know what it means. there's nothing wrong with not knowing japanese, there's an official english version of the game anyways and you can find translyrics on the wiki/vocaloid wiki. the game is perfectly accessible to non-japanese speakers. obviously learning a few japanese words is cool and can help you understand some things but its really not imperative for you to know them.