Our daughter and I have been watching a Scottish sitcom on Netflix, as well as a few British sitcoms. They're all really funny, and I think funnier and better than American sitcoms.
Besides the plots, I find the accents very interesting. We have to watch them all with the closed captioning on. Our daughter was down the hall and heard the dialogue for the Scottish show. She said it sounded like a foreign language to her, because she couldn't see the words at the bottom of the screen.
They might speak English but it's not the norm. For example, in the Scottish sitcom, they might say, 'Innae ye frae doon the street?' That means, 'Aren't you from down the street?' They also call a woman a 'hen.' In the British ones, I've heard words like 'chuffed' (means excited, I think), and quid (pound). I've resorted to looking some of the words up while watching the shows, just to figure out what's going on.
When I worked on my Scottish Football Series, I did a bit of research into the language. I didn't put a lot of the different language into my books, because I didn't think Americans would understand it, unless they'd spent time in Scotland. Even so, the language is gorgeous to listen too all over the U.K. I even find myself slippin' a few wee words into my brain once in a while.
So, when you're writing a different language or dialect, don't inundate your reader with difficult to understand words. Slip them in every once in a while and your reader will thank you.
Have a great week!