In this book a number of dialects are used, to wit: the Missouri Negro dialect; the extremest form of the backwoods South-Western dialect; the ordinary "Pike Country" dialect; and four modified varieties of this last. The shadings have not been done in a hap-hazard fashion, or by guess-work; but painstakingly, and with the trustworthy guidance and support of personal familiarity with these several forms of speech.Having the dialects all spelled out in the book was very distracting, and makes the book a chore to read.
I make this explanation for the reason that with out it many readers would suppose that all these characters were trying to talk alike and not succeeding.
Dialect and accent is one of the biggest way that people know "you're not from around here". If someone of a different ethnic background starts talking exactly the way you do, they're automatically "one of us". If you talk "funny", you put yourself in the "one of them" category.
Dina Titus ran into that problem when she ran for Governor a couple years ago. A conservative political group mocked her accent in a famous televison ad.
Some authors use dialect as a way to establish a character's background and personality.
Most authors use some dialect, but don't spell out the entire sound of the conversation.
People run into dialect differences everywhere. I remember a story about a woman who moved to New York, and the locals were complaining about the high cost of thing, saying items cost "A nominal egg." Since the price of eggs was going through the roof at the time, it took the unwary newcomer a long time to grasp that the locals were actually saying that things were costing "An arm and a leg."
Do you think that the dialect in Huck Finn added to the book? I've heard in various places if someone with a heavy southern accents starts talking, people will automatically perceive that their IQ drops by 20-30 points. Do you think this may have been Twain's way of stereotyping most of his characters as being not terribly bright?