When readers think of dialect, they tend to think accents.
An author might say that a visiting grandfather has a strong southern accent and then throw in an occasional y'all. Or the choice could be to emphasize every southern inflection. "I'm not sure what you people are talking about" becomes "Ahm not sure what y'all are talkin' about."
I tend to work first with word choices. For example, in the Midwest, a house could be referred to as of frame construction (wood as opposed to brick), while in New England that's a clapboard house. And how is it pronounced? It's clabberd. That's not a word I would spell phonetically, though when working with a narrator for an audiobook, it's a word I'm sure to check.
When deciding how much local dialect to include, I think of authenticity and distraction level. I want to recognize there may be a distinct way of talking, but I don't want readers to get tired of constant spelling variations. I also don't want readers to spend time critiquing how I chose to portray a speech pattern. I want them to focus on the story.
Critique groups and beta readers are great resources for assessing speech patterns and word choices. I wish I had a dollar for every time a critique group member said, "They wouldn't say it that way." I could buy a new car. Or go to six writers' conferences a year.
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