Actors are good at this sort of thing

Good question. I find it easier to do different English accents, for instance, than, let's say, a European Portuguese accent (my native language). I don't know why. I'm not saying that I could do different accents in English perfectly (most of them are lousy but still recognizable, others are more convincing but still), but maybe since English is a foreign language to me I can experiment with it more easily. Anyway, I think that doing different accents is quite fun and good practice for advanced learners, as they make you pay attention to phonetics, intonation, and even vocabulary itself. Cheers!

A read an article about this the other day. It takes either a very long time spending time between natives to pick up the accent but it will never be perfect as long as you didn't hear the same tones when you were still a little child. In school the teachers teach British English to us ( Dutch ) people, but tv shows us American movies/series. So I've a mixture of both to be honest. But apparently it's all in the childhood