Aratrea wrote:
Just for the record, actual Medieval English is more like Middle English, which is basically unrecognizable to modern English speakers. So if your only concern is authenticity, then I'd say no.
Using KJV-English adds a distinct flavor to the speech in your book, which may be beneficial or not beneficial to the story, depending on the author's preference. I don't think it's necessary to use it in your book. However, if your characters are using a lot of modern slang in a medieval world, the reader may be scratching his head...
Totally in agreement with both points here.

I would add to this that using any sort of "unusual" slang or accent can be a hindrance. It's not the way your readers think, so it will be hard to get into a book written in that form. If I personally were to pick a book off the shelf thinking "Hm, Christian Fantasy, looks good" and opened it to the first line and it read like King James my reaction would be wide eyes, a squint, a shake of my head, and a book that ends up returned to the shelf. *shrug*
Now, that being said, it would be perfectly all right to give a character an old fashioned accent or other inflection of speech in their dialogue

--again, if it's not too distracting for the reader. For example, I love Brian Jacques' "Redwall" novels, but even in them, sometimes the accents are a little too much, too heavy, and it distracts from the story.
So. Basically: Write the way
you feel the story should be written, if that's what you're going for. Doesn't matter the form or style or the words you choose. Still, If you're writing to be
read, you should keep the readers in mind and if the reader doesn't want to sit through four pages of Old English narrative, then maybe you should consider a different route.