I actually grew up with an ear for language, including sound variations and accents. Wherever I happen to be, I readily assimilate the patois of the area. In New York, people accept that I am from their borough, or whichever borough I choose to mimic at the time. In the south of Ireland, I am accepted as a local and everyone wants to know whereabouts I live. In Toronto, Atlanta, Los Angeles, Chicago, and Vancouver the result is pretty much the same. In college, I had a Spanish teacher from Venezuela. He wondered why I was taking the class because he thought I was a native speaker. (3 yrs of Spanish in high school helped with the language section of his confusion as I spoke rather fluently (needed the foreign language credits for graduation) but my ear for mimicry was impeccable.) I used to tell people that, while other kids were collecting dolls and stamps and Matchbox racers and whatever, I was collecting accents. And it's true. Sorry for wandering there...
back on track:
Sort of like that "ar" sound some mid westerners put in the word "wash"? It would be annoying to read a novel where a character was from one of those regions, and every time that person said "wash" it was spelled "warsh."
And yet, in the southern US, that pronunciation would be "worsh". And they pronounce the word "I" in some strange variant where it would be extremely difficult to provide an accurate phonetic transliteration. "ah"? No. "eh"? Nope. "aey"? Well, getting closer but... nope. Imagine trying to say the word "I" with your mouth open wide but twisted in such a way that your upper teeth go one way and your lower mouth/jaw/mandible go in the other. THEN try to pronounce it without closing your mouth. THAT's sort of the way it is pronounced. But, you can't put all of that into your story just to get the regional dialect accurate.
"...he pronounced the word "skeleton" as... "skel ee ton" instead of "skel uh ton." (long e instead of short e for the middle syllable)."
And yet neither of those is the pronunciation I grew up with, which was more like, "skel eh ton" and/or "skel ih ton".
Except Canada is a big country too, and I doubt people in Ottawa talk exactly the same way people do in Toronto or in Vancouver.
All of which brings me to the purpose of my post. People have a different 'ear' for speech, based on where they grew up and how they learned to speak and, too, whether the language you are writing is a first language for your reader. As Roxxsmom noted, everyone has a different understanding of language and trying to create that same accent for people who would well be hearing it in a different way would be difficult.
So, the trick is to put enough of the local patois into the character's speech to provide the essence of that accent without so much as to make it hard for the reader to read. Sometimes, you can simply allude to the accent and just let it go at that.
The trick is to put enough of that accent in to give the character flavor but not so much that it is going to make the reader stumble over the reading and break the rhythm of the sentences.
