Well, I made a major decision as I wrap up my current book. See, the nature of the world in this book makes it likely that one would meet people from all over the world, and from lots of different eras. My main character is American but of Mexican descent; a supporting character is Spanish of some kind, and another is Scottish; lesser characters are Southern, Persian, British, and others. Not all of them speak English, but most of them do. That means a lot of accents to understand and apply, and besides the accents you have idioms unique to the individual culture. This is tough.
What I did while writing the book was write each character the way he/she sounded in my head, and for most of them this worked well enough to get the accent across. My Scottish guy was the exception.
He never sounded Scottish to me. I really really wanted him to be Scottish. Really really. However, although I'd decided he should be Scottish, I'd done very little research on how to actually make him seem Scottish. I thought I'd be able to layer it in at my leisure. I'm finding it's not that easy. Also, there's no real reason to have him be foreign, except that I wanted lots of different places represented.
So now I'm on the verge of completing the book, and changing "your" to "yer" ain't gonna cut it. And I started asking myself, "If he didn't sound like a Scot in your head, why did you make him one anyway, you dimwit?" And the answer is, I didn't. I didn't make him a Scot. He's an American who sometimes says "wee lass" and "are ye out of your mind?" See? Now, I could go and make that "are ye out o' yer maind?" and that would be fairly Scottish. But to go back and spend an extra month to add that accent to an entire character's worth of dialogue wouldn't have a good cost/benefit ratio.
So Caellum is now Scottish-American, if there is such a term. He's still a rakish musician, still mysterious, still over-sexed, but I think he'll be relieved to stop speaking with an accent. He wasn't very good at it.