I think about this sort of thing a lot in my fantasy and sci-fi writing. I really liked how in Firefly they used the word "goram" in place of "god damn". And it worked because they used it consistently across multiple episodes, so the viewer was able to pick up on it. Now, in the case of that show it was most likely done to beat the ratings board for TV standards of the time, but it did inspire me to think more about slurs and cursing in non-realistic settings. In my fantasy series, there are slurs that people use for different races (as in elf, dwarf, giant, human). And characters also use the more cliche "by the gods", but I think it makes sense in my world, because religion is a major thing in the world for many characters. In my sci-fi novel, "by the goddess" is used, because the MC has literally met a goddess. I think it doesn't so much matter what words are used as long as it's consistent throughout the work(s). The Dark Tower series plays around with this idea a lot, because it's clear that the real world and the fantasy world are linked in various ways, but they are not direct 1:1 mirrors of each other. So some things are consistent between them and others are wildly different, including how language is used.