Sanchezman a surprising amount of people (myself included) when we're looking to find a game to buy/download the first thing we look at (besides the trailer) is the rating.
Is the game E, T, or, M and, if it is T or M, we look up why. There are certain T rated games that to certain people should be rated M and there are other people who think vice-versa
Anyway if some people can not really go on without without the NPC's swearing I think the best option would be the fake slang and swear words but, if that doesn't work than why not put a toggle in the options menu to turn on and off the swearing.
although could put a little humor in the game make certain characters instead of swearing make a vague(or otherwise) reference. We could use it to give certain people who have been indispensable to the world of science fiction a little credit. such as
What in the name of George Lucus's Astrodroid is going on.
Isaac Asimov's Keyboard, What happened!?
and so forth
Chess is a sport. A violent sport. - Marcel Duchamp.