Dialect and Dialogue
My son is currently reading Mark Twain’s, The Adventures of Huckleberry Finn, for school and immediately began to comment on how hard it was to read because of Twain’s rendering of the local dialect. I took another look at it then and, much as I hate to say it, he’s right. More than any of the other works by Twain, this book is made more challenging by excessive use of dialect and incredibly bad grammar. Granted, it’s written in Huck’s POV, but Twain was a little too dedicated to the idea that Huck was uneducated and, shall we say, rough around the edges. The style get’s in the way of the story.
I am sure some of the examples from classical literature use dialects, including coy, phonetic spellings, to convey the sound of regional speech to those who hadn’t heard it before. This style of writing is more difficult to follow than trying to understand a thick, unfamiliar accent when spoken. Trying to read that kind of thing is like decoding a foreign language. It takes away from the story you are trying to tell. These days it should be avoided, since most people have at least some exposure to different kinds of speech. There are better approaches to the problem.
You can convey regional (or uneducated) flavor by word choices and syntax without resorting to an attempt to write words the way they are spoken.
“Lordy, child! Get in here and get out of those muddy things before your mother gets home or she’ll skin you alive.” - Now just try to read that in anything other than a Deep Southern drawl and get automatically sounded like git.
“John Micheal, I’m thinking it’s to the pub we’re going.” This one is equally obvious as Irish brogue and I’ll bet you rolled the ‘r’.
Syntax and word choice. While some of the grammar may be unorthodox, it’s not actually incorrect. The word choices and syntax alone carry the dialect without being unreadable.
We also need to be careful how we render dialects or the sense of someone who’s first language is different. I say different, as opposed to not-English, because, if you want to get technical, none of the characters in the Talmanor series would actually be speaking English. Selarial speaks Common quite fluently, but you will see a shift in syntax if she gets angry. It signifies the natural tendency to make that kind of linguistic slip under stress. If you have a character with incomplete command of the language, syntax and word choices can go further than any other technique to convey that circumstance. Real people do it everyday.
Should you ever write coy, phonetic spellings and horrid grammar? Of course you should! Just keep it limited to small doses in strategic places.
Please note, I happen to love Mark Twain’s writing. That particular book is just difficult for anyone over the age of eight to read. 
