How International is the English Language?

I'm used to rejection. It's part of life being a writer and in fact I can see a lot of value in the 'aim for 100 rejections in a year' idea. However, the best rejections offer constructive criticism or are neutral in tone. Today I received a really rude rejection from an American editor who suggested that though 'people in Scotland may speak like that' people in America would not want to read it.

Now I accept that there may be good reasons that my story didn't get included in the anthology in question but this is not a good reason. 

The characters are Scottish, the setting is Scotland, sometime in the medium future. There are three styles of speaking in the story, there are those who speak an urban Scots-influenced English, those who speak a Western Isles style of English influenced by the rhythms of Gaelic (the first language of many people in those islands) and there is a character who speaks a very careful English because it's his second language and he doesn't want to make errors. All the ways of speaking are slightly different than they are now, because, well it's the future and language changes.

I haven't included swear words or particularly obscure Scots words and I've kept all elements of Scots in the dialogue, rather than in the narrative. To my eye, all the characters speak a readable form of English, with some influences from Scots and the rhythms of Gaelic. This makes the characters more individual and adds authenticity to the story. After all, people in Scotland don't actually speak like Americans and I certainly don't want to think that in the medium future, we'll all have, like, American accents.

Why shouldn't Americans want to read this? After all, Scottish cinemas show loads of American films and we have to listen to accents and dialects from across the States. I can't imagine a British editor would tell an American writer that they couldn't accept a story set in America because the characters sound too American!

People have different ways of speaking and reflecting that in fiction is surely a positive not a negative.