I’m a big fan of Japanese dialects, or hōgen (方言) and have been researching them for years. Japanese often ask me if there are dialects in English, too. The answer is yes and no.
While there are some regional differences in vocabulary and phrases (and slang in particular), English grammar does not change very much from country to country. Because of this, a Canuck (カナダ人) can understand a Kiwi (ニュージーランド人) and a Scotsman (スコットランド人) can converse with a Yank (アメリカ人). Actually, the American might have some trouble understanding what the Scotsman was saying because of the accent (訛り).
It is the differences in accent and intonation, more than anything really, that change from region to region. Below are some videos produced by a good YouTube channel called English Like a Native which highlight differences in accents. Have a look. (The Glaswegian, or Scottish accent, is the most entertaining.)