Have you ever seen "Das Boot?" The original in German, not English. What about an epic martial arts movie that is in Chinese? Point being, only a part of the world speaks English and not much of it speaks proper English (any Welsh or Scots care to chime in?). More to the point, though everyone hates reading subtitles, you tend to get a sense that you're witnessing an actual piece of history, almost as though seeing events happen through some magic time machine viewer.
In the 1870's Western I wrote, using Old West slang, Chinese, French, Spanish, German and numerous Native American names and languages made it "in my opinion" read true. I've had many people since ask me if that
purely fictional story was actually a
factual accounting due to that (along with so many little known facts of the region and era). That's a nice compliment IMO, when a fictional tale is so spot on that it reads as historical fact to many.
That said, if what some are suggesting, that made up names/words make it unreadable, then let me just say my latest work would drive you insane
In that work, I have TWO made up pidgin languages, and an alphabet. There is also an entire system of government and a system of population management that intentionally twists terms and word meanings to imply innocuous intent. Finally, there are numerous nationalities of people in the story who all mix English with their language.
Is it more difficult to read? Yes, yet if you get into it and the names/language/etc. are logical and there is a means for you to understand it, 'I believe' if done well, it can make the story more convincing and immersive.
So, I guess it boils down to this... Do you want the reader to feel "that was a good story," or do you want them to feel "this could be real?"
Just the opinion of a novice,
K2