A hard linguistic question

Last Wednesday, a student asked me, in English, about what dialect, he didn’t used this word but recursion ahead I’m using it, of English is the most difficult. Naturally, I said no one. He was asking me if I find British, American or Australian dialects difficult or which one is the hardest to master. That made me think about one thing I want to write about. What's the correct distinction between dialects? Is it only nationality that matters? I don't think so. What really matters is the speakers. I mean the way they speak. I mean where, exactly, they live. Thus, can we talk about a dialect in terms of countries or in terms of cultures yet districts or provinces? Culture matters. A country is not a culture itself yet a region that includes a lot of them. A lot of cultures that coexist together in a place called a country i. e. Peru, the USA, etc. A dialect is the way how a culture speak a language. How they express themselves in a language. Which one is the most difficult, Aaron? I have no idea, in that very three countries are a bunch of dialects that I don't even know. Hard question of yours.