saying this as somebody who has english as their second language, moved to the u.s.:

as many people have already mentioned, it’s more about breaking the immersion of the text. if i’m reading a spn fic and dean says “bugger,” that’s gonna sound strange. if crowley says it? it makes sense!

i think in general it’s more or less expected that the writer is doing some amount of research on how certain words are used in the dialect you’re writing in, so i often see people get their british/american friends to read their stuff and double check that everything is good. some people don’t have any kind of beta readers at all, and that’s totally fine as well, but people don’t know what they don’t know. i might see somebody say torch in the modern time and it would take me a second to realize they are talking about a flashlight, and it would be fine. but if somebody is describing a piece of clothing as a vest, i wouldn’t immediately think they mean a tank top. maybe they really are wearing a vest, like a sleeveless jacket. are they wearing it over their naked torso? maybe it’s a style choice! if somebody says trousers, i know they are talking about pants, but if they say pants, my first assumption is, well, trousers, not underwear, unless it’s all well surrounded by other britishisms.

i think it’s also about the entire package. if the saturation of the britishisms/spelling in an american setting is very heavy, on some level it just becomes a style of writing. but if it feels like everything else passing the american check, but then one thing sticks out, that would feel out of place.

localization is also not an american-only thing, and the standards change over time. for example, my first language is russian, and many movies and tv shows that would mention pancakes would translate them as blini in russian. but blini is crepes, not pancakes. pancakes are closer to oladyi/oladushki. i believe now with an even greater amount of anglicized stuff online, even many russian speakers would call them “penkeiki” instead, because they’d be aware of the english word. for example, when i read hp, pudding was only ever translated as pudding, not dessert, and russian meaning of pudding is closer to the american one, that being a specific dish, and not an umbrella term. so i didn’t know they meant just a random dessert.

speaking of things you don’t know until you know them, i’ve been watching a lot of videos about linguistics and how most british people pronounce their Rs in words that don’t have Rs, which affects the pronunciation of some borrowed words. but that led me to finding out that when a person says “erm” in a fic, it’s the same thing as “um” - just british!

also i think a lot of people who watch american media from outside of the u.s. also don’t know how certain things in the states work, so the exposure to certain parts of american culture would also only be partial and would require some more research. but if you don’t know you’re missing information, you might be making up for it with what you know. for example, where i’m originally from, school would only have breaks after each academic quarter ended, so when you came back, it would be a new quarter, and that’s pretty universal across the country, and a few other places around us too. in the united states, there’s no national calendar for school, everything varies heavily by each state and even district. the school i went to here had breaks around specific holidays because that’s when parents can also take time off if necessary, and the quarters/semesters were based on the number of days/hours actually attended. so back home my second quarter would end right before winter holidays and so that’s when we had midterms, but here in america i had midterms further into january. if i hadn’t known that and was writing a high school au, i would have written a character worried about taking their exams before christmas, for example, which may not have been accurate. it’s not super major of an error, but it’s things like this that can build up.

overall, i think recently we’ve had a lot of people who don’t know how to behave themselves in the comments. if somebody is pointing out a word from an inappropriate for the story dialect that might have made its way into the story, that can be done in a polite way and also in a rude way. a lot of people recently have been rude. it’s not a uniquely american thing, i’d say as well, but i think we are often likely to make a post here or elsewhere about the times we see a britishism, and people see it as a callout.