A lot of would-be authors don’t understand the difference between an accent and a dialect. An accent is a way of pronouncing words. A dialect is a way of choosing and arranging words which characterizes a subgroup of a language’s speakers. Writing in a dialect is legitimate in fiction or when quoting real people. Trying to write an accent is usually a mistake.
Let’s look at a typical passage from Mark Twain’s Huckleberry Finn. That novel is full of dialects, but notice how he writes:
“I wish I knowed, but I don’t. I had it, because I stole it from them; and I stole it to give to you; and I know where I hid it, but I’m afraid it ain’t there no more. I’m awfully sorry, Miss Mary Jane, I’m just as sorry as I can be; but I done the best I could; I did, honest. I come nigh getting caught, and I had to shove it into the first place I come to, and run — and it warn’t a good place.”
This short paragraph contains many forms of word usage that are incorrect in standard English: “I knowed,” “it ain’t there no more,” “I done,” “I come” (in the past tense). It doesn’t contain any indications of nonstandard pronunciation, with the possible exception of “warn’t,” which could be considered a dialect word. When I read this in my mind, I can’t help but hear it in a Southern accent, as will most readers. But the accent is only implied by the word choices.
If Twain had written the accent, he might have used spellings like “ah” for “I,” “mow” for “more,” and so on. It would have made the passage look ridiculous and wouldn’t have captured the way people like Huck talked. English spelling doesn’t have the tools to represent an accent realistically. Trying makes the text hard to read and seems to mock the speaker. Some writers resort to misspellings that don’t even reflect the pronunciation. This turns up a lot in the old minstrel-show song sheets. For instance, the song “Jump Jim Crow” (warning: offensive lyrics) uses “weel” for “wheel” and “galls” for “gals.” The underlying message seems to be that these people can’t spell properly while they’re talking, as if that made any sense.
To take a less remote example, imagine portraying a Bostonian saying “There’s no place to pahk my cah near Hahvard Square.” It would be ridiculous to write it that way.
Portraying a dialect is legitimate, as long as you do it right. Badly written dialect turns into caricature, but writing it well can add to a story. Make sure it’s necessary to the story, and don’t overdo it. Heinlein’s The Moon Is a Harsh Mistress creates a dialect for the lunar dwellers. It helps to emphasize the contributions of Russia and Australia to the culture portrayed there. As with anything else, the more you know, the better you can write it.
If a character has an accent, usually it’s better just to say so rather than trying to write phonetically. A small sample may help to make the point, but don’t go on at length. You’ll just make your writing hard to read.
Here are some pieces on the subject: