I have been using captions on Netflix and Prime a lot lately. And have noted when they do (or do not) indicate in the caption when speakers elide letters. (As in the example, do the captions say "gonna" or "going to" when what was said was definitely the former, etc. Do the captions reflect accents, real (either of the actor or the character) or temporary (like funny voices when a parent is reading a book to a child), and so on.) It's quite interesting.
Do you have opinions about spelling those out in, say, a novel or short story?
Personally, I find it very hard to read dialog that is attempting to reflect the accent.
In Philip Jose Farmer's Riverworld books who spoke with a lisp. Farmer insisted in writing all of his dialogue with the lisp preserved. He was a fairly major character. It was maddening to me when I read the books in late grade school/early junior high.
I loved those books, but recognized that they were pretty badly written even at the time. I had a lot more patience for bad writing back then, apparently.
