>But once "thank you" is said, most people awkwardly respond with "ah", because there's no phrase in the language for "you're welcome".
In London I've noticed that instead of saying, "you're welcome" people prefer to say "no worries", which is far more casual. I don't know why that phrase started to be used but if I had to give a guess I'd say that it was out of awkwardness because there wasn't a less formal/personal response to use.