The comments on this are fascinating. I recently betaed and Yankpicked a 110k fic for a couple of authors from New Zealand, and the process involved a lot of "wait, you don't say that? REALLY?" moments from them. There were a lot of instances of the word "ages" (as in a thing taking ages to happen), which I suggested they replace with "forever," but they weren't quite satisfied with that as an equivalent. They used "though" in contexts most Americans wouldn't, and "round" instead of "around." And I found a lot of phrasings that weren't strictly un-American, but that I would expect to hear more from older adults (this was a hockey RPF fic, so the POV character and most other main characters were young men), or that I do hear, but much less often than the NZ folks used them. For example, they would use the word "so" as a superlative without a subsequent "that," e.g. "he's so anxious"--which we do once in a while, but I don't see it here as often as it cropped up in the fic. I should have kept a list as I went, because I know we discovered a lot of interesting differences in language habits that I've now forgotten.

When I have some free time to spend transcribing and analyzing YouTube interviews, I'm planning to pull together a post on language patterns of Russians speaking English as a second language, because hockey RPF fandom has a lot of Russian characters and a lot of authors who can't write their dialogue believably. (This includes myself; my main reason for doing this is so I can include Russian characters in my own fic without freaking out too much about getting their speech patterns wrong.) I think that one Sherlock fic is the only time I've really made an effort to Britishize (Britishise?) my writing--I didn't have as many Britpicking resources or as much commitment to quality in fic when I wrote in other non-American fandoms.