Once you start spelling words in dialogue phonetically and loading the page with apostrophes, you won't be able to stop. Notice the way Annie Proulx captures the flavor of Wyoming voices in her book of short stories Close Range.
This rule is particularly important for writers like me who live in a foreign country. If the story contains foreigners, you have to sprinkle it with foreign words, and sometimes try to represent the accent.
In the group of short stories Leonard mentions, the flavor is achieved, for example, by dropping a few g’s and saying “was,” instead of “were.”
In his novel And the Ass Saw the Angel, Nick Cave writes a story that takes place in the deep American South. He achieves the southern accent simply by replacing “I” with “Ah,” and “my” with “mah.” To me, it worked. It was not overpowering, and it got the message across. That novel, by the way, is one of the best works in any language I’ve ever read.
In Lionel Asbo, Martin Amis has to get across the working-class lingo of Lionel without making the thing unreadable. For example, he uses “you,” instead of “your." But one thing that’s always an issue, is how to get across a speech impediment the character has, or just a constant mispronunciation. If you wrote it the way the character said it, the reader may not understand what you mean. Amis does it by writing it correctly, then putting in italics how the character said it. To wit:
“Where you off to now then?”
“The Pantheon Grand.” The Pamfeon Grand.
Works for me. That’s pretty much how I dealt with using Italian in A Beast in Venice. If the phrase would not be immediately understood by the reader, I put the Italian in italics, and followed it with the English translation. As to the Italian accent, I just left out a connector here and there: “Brig, you a funny guy.”
In contrast to these novels, where the effect is achieved by a few touches of the language or accent, Anthony Burgess, in A Clockwork Orange, created a whole system of slang based on Russian. The first time I read the book, there was a glossary in the back. Behold:
All the time we were sirening off to the rozz-shop, me being wedged between two millicents and being given the odd thump and malenky tolchock by these smecking bullies.
The interesting thing about this book is that it never would have been known in this country (USA) if it weren’t for Stanley Kubrick making a film out of it. The film is a masterpiece, but the book is a work of genius. Once you get used to the slang, the language is delightful and full of humor.
By now you should be able to see why one of the bits of advice all writers give to aspiring writers is to read a lot. There is something to be learned from every book.