You can tweak things just a bit without getting unintelligible. Like Mad Max: Fury Road using chrome as an adjective. Firefly uses shiny a lot to mean good in general.
Well, that's not an accent, that's vocabulary, and plenty of shows do it, often to bypass censors. See Farscape's frell, frack. It's done in video games too - for example, 2077 has a pretty rich vocab
“A Clockwork Orange”, famously, was set in a post-Cold War setting where the West and Russia had grown close, and the who,s thing was written in a dialect that was part English and part Russian. But I agree with the other poster that in general it’s too much work.
A creole is what happens when several groups with different native languages are put together and have to communicate. If you have people speaking the same native language in isolation you will eventually get a distinct dialect of the parent language, not a creole.
I thought that was pidgen so I looked it up if anyone is curious:
What is the difference between pidgin and creole? In a nutshell, pidgins are learned as a second language in order to facilitate communication, while creoles are spoken as first languages. Creoles have more extensive vocabularies than pidgin languages and more complex grammatical structures.
The Belters were subjugated, but not isolated. This is shown with a lot of the "security forces" largely being Earth/Mars based but also just general trade. Much like with the very large physiological differences (mostly in the books and season 1 of the show), ~100 years (since the Epstein Drive was invented 129 years before the protomolecule and it looks like Ganymede largely required it to be "colonized") just isn't really enough for that kind of divergence.
The "oriental fetishism" of Firefly/Serenity is a lot more likely with mostly being a hybrid of different languages based on who the original colonists were... and that was a much larger period of time with even more isolation which is just funny.
Also, this ignores regular communication and media sharing between The Belt and The Inner Planets. Like, there have been some interesting studies that point out how pervasive "california english" is becoming because of "hollywood" (which films everything in Toronto). So even the Belters who more or less live in a mine their entire life would likely still watch documentaries from Oliver Queen's baby mama and whoever Mars's equivalent of Kim Kardashian is.
A lot of it boils down to the idea behind what a translation actually means.
One school of thought is that you do word for word translations. So you get very strange sentence structures and direct translations of idioms. Think the idea of (apologies to the French, it has been over a decade since I tried to write or speak any of it) "Il est drole" being translated to "He is to be funny" rather than "He is funny".
The other school of thought is that you care about the meaning of the text and not the word for word translation. So that involves a LOT of updating/adapting idioms but also names. Among the weeb crowd, people lose their god damned minds any time a character has their name changed. But you get into a mess where "Hikari" is not meant to be an "exotic" name and is really being used closer to "Fred".
I remember way back in high school we specifically read a version of Beowulf to demonstrate this. It involved the "original" Old English, a direct translation that is somehow even harder to parse, and then a version written in modern english.
And that is the basic idea. It doesn't matter if Basic is English, Chinese, Russian, or (most likely) a hybrid of them all: What matters is that the reader/viewer understands what is going on and can appreciate the references.
Another example that usually comes up is how the movie A Knight's Tale is one of the most "historically accurate" adaptations ever. Because yes, we have crowds of peasants singing Queen songs and Nike swishes on armor. But... that is a lot closer to what tournaments and jousting were than people playing equally inaccurate classical music. And I've made similar arguments for the god awful Romeo+Juliet where Luigi and Leo wield "sword 9mm" pistols.
In the novel I'm writing this occurs. Someone from 2004 is transported to a planet in the year 240,000. She learns the language, but she can't quite get the dialect down because humans have evolved different facial/vocal muscles by this point.
Obviously it's in writing so I can get away with not having to explicitly define the accent. 😅