Okeydokey. I'm kinda irritated right now, so there will be colloquialisms out the wazoo. You have been warned.
Anyway, this story I was reading about some superheroes that team up with angels to bring down badguys from Hell (literally) was really good. The author, who was posting this story on a fiction site, wrote really, really well. Spelling errors were minor, their grammar was usually good (and who's perfect with that, anyway?), and their writing style really sucked me into the story. They did a lot of research, too; they really knew their Demonology and Angelology, and I almost wonder if the person is Greek/Eastern Orthodox because they knew so much about what the Orthodox branch of the Church says about Heaven and Hell and such. (Rosie is a theology & Church history nerd. I occasionally nerd about mythology and other religions, too, but that's beside the point right now.) They also wrote the angel and demon characters--and other religion-related stuff--in such a way that it didn't make me, a very devout follower of the Wesleyan Holiness tradition, twitchy. I didn't even really stop to think about it until I got distracted from the story. That is an impressive feat, actually.
What did bug me was that her very American superhero characters (they were headquartered in New York) were using slang and other terms that I, Ms. Language Dork Extraordinaire, who reads both collegiate and slang dictionaries for fun, had never heard before. I dismissed it the first few times, thinking that it was just something from a region I haven't gotten around to studying or something. I seriously doubt any single individual knows every American English slang word, anyhow.
I stopped dismissing it, though, when a couple of the guy characters got into a fight over whether "footie" or hockey was better.
...Wait. Excuse me--"footie"? Really? I made the connection right away. Footie = football. However, it was clear they were not talking about American football, but what everybody else and their dog calls football and Americans (and Japanese, now that I think about it) call soccer. Even if that were not the case, no self-respecting American guy would ever call their beloved rough-and-tumble rugby derivative something as cutsie as "footie". "Footie" is a word used to refer to pajamas with feet ("footie pajamas" or "footie jammies"), or occasionally that game your play with your honey under the table or on the couch, commonly called "footsie".
Now, I can see a British guy pulling it off. The UK is the home country of certain guys that somehow remain completely and utterly masculine wearing polos in public (while not on a golf course), sipping tea with an extended pinky, eating crumpets, and carrying handbags. Footie is often used to refer to Association football, the kind where you kick around a black and white ball and try to get it in the giant net. Aussies use the term (also spelled "footy", apparently) for various kinds of football, including Aussie rules, but Aussies--guy, gal, or dancing bear--can get away with calling it anything with those accents, in my humble opinion.
I read a bit further in the story, and sure enough, more words popped up: "pram" for baby carriage and stroller, "boot" for car trunk, "bonnet" for car hood, etc. There's not enough to tell whether the person is from Australia or Britain (or perhaps New Zealand?) I can navigate because I know a certain amount of the British dialect (I read a lot of British literature in high school), but it's annoying enough that I just stopped reading the story. The characters are NOT originally from Britain or wherever, which would excuse the word swaps, but were specifically stated to be "American" and a few were mentioned to have been born in American towns. It's driving me crazy and it drove me away from the story, which is a pity.
Lesson to take from this little experience: please, please, please research the dialect of English (or whatever language) in the country your character is from. Find an online dictionary, watch a few YouTube videos from natives to study general speech patterns, whatever you need to do. Using slang from one region in another is one thing--people travel all over the place--though I'd research that too, if you want to keep it realistic, but mixing up dialects is another. The average New Zealander is going to have no idea what you're talking about if your character is speaking South African English, and that's a problem if said character is supposed to be born and bred in New Zealand.
Oh, and spellchecker won't always help you with different spellings, by the way. It's useful, but, well...Mine's currently telling me that the "Zealand" in New Zealand does not exist as a word, if that gives you any idea.
'Kay. Enough ranting. Next one should be that "more about me" one I talked about, but we'll see.