...and I take my whisky neat.
No, no, not trying to get you to change anything. I want to talk about language in fantasy and sci-fi (and other other-worldly, other-timely) settings.
We take it for granted, we writers, that most people have the same feelings. Not about the same things, of course, and the way people - characters - express their feelings can vary. But everybody feels some way or other about what's going on around them. (Yes, even Spock.)
How they react is going to depend on who and where and when they are. Unpleasantly surprised or confronted, I myself might say, "Shit!" but Scarlett O'Hara, or Commander Deanna Troi, would not. And while Cmdr. Troi and I might both say "Okay" to something we approved, Miss Scarlett would not.
That most cultures through time have their formal and casual sides doesn't mean that those formalities and informalities are or should be expressed the same way everywhere/everywhen. Example: if I'm reading high fantasy, I do not want my Elvin princess saying "Okay" to anybody. Period. That's a modern colloquialism that does not convert. (So maybe yes, I might want to you change some things. If your Elvin princess talks like a Jersey girl, I want you to change that - but that doesn't mean you can't change it to her having been brought up cross-dimensionally in Jersey.)
In the sci-fi/space opera I am currently converting to Kindle's format, my characters live 500 years from now, in the United Galaxies; Humans are no longer the darlings of the spaceways, but English is still a well-known and widely-used language, and some ancient slang is still common. So sometimes, they do say "Okay." But the Oldeveni in another dimension they end up visiting, even though they live only slightly out-of-phase with 20th century Earthlings, don't - because they and their cultures are the source of our high fantasy.
I get that urban fantasy mixes the formalities of other worlds/cultures with the informalities of ours, but not all fantasies are urban, just as not all sci-fi is hard science. All I'm asking is that people be aware enough of their genres to keep the language and customs and habits in their stories consistent, internally consistent. If that requires a change, then yes, I am asking you to convert!
Oh, and one other thing: I promise that if I read something of yours and see an incongruity of this sort, I will contact you first, and not make it the focus of any review I write, so I'll ask the same of you in that regard, too.
Write on! (and read on!)