When a book is set in another country, another world, or another universe, do you expect the characters to sound like they are from the good ole' USA? Think about it-- you have a big game hunter from Australia leading a band of multinational vacationers in search of lion on the plains of the Serengeti accompanied by trusted native bearers, wouldn't it seem odd if they all sounded like they came from Brooklyn? Sure it would! So why is it some editors try to Americanize every book their hands touch? I don't get it, do you?
Not all do.
We have several members from elsewhere in my critique group who have no issues with editors wanting to change their work to suite the "home town crowd".
All they ask is for the spelling to be ours so the reader won't think it's a typo. Understandable. If the book is set in England, then English slang should and will be used. If on the Delta 3 in the fourth quadrant of the Planetary Alliance, they speak Deltanese and serve Whamphor entrails each lunar solstice, so be it. Fried cat fish and mashed taters are unknown on that planet. You, the reader understand this, right? If everything is as we know it, what's the fun of reading about it.
When in Rome do as the Romans, when in Australia, cooked chook might well be on the menu. That is the way you want it, right?