She Said, He Said

Many great authors write great dialogue: Dickens, Hemingway, Twain, Sinclair Lewis, and Steinbeck to name a few. Talking to the reader through characters is an art. It's not always what they say, but what they imply by those carefully phrased words that matters most; think of Tom Joad's soliloquy at the end of The Grapes of Wrath: 
Then I'll be all around in the dark - I'll be ever'where—wherever you look. Wherever they's a fight so hungry people can eat, I'll be there. Wherever they's a cop beatin' up a guy, I'll be there... I'll be in the way guys yell when they're mad an'—I'll be in the way kids laugh when they're hungry and they know supper's ready. An' when our folk eat the stuff they raise an' live in the houses they build—why, I'll be there.

Yet, colloquialism, accent and turn of phrase are equally important, they are the mechanics behind the message, and they need to mesh. For instance would it make sense if a character who is British said: "I'll need to pop the hood to check the oil".  Shouldn't the Brit say, "I'll need to have a look under the bonnet to check the oil"?

It can be a tricky thing to write in the vernacular. Twain was a master of any region; Steinbeck as well as Faulkner were adept at Western and Southern drawls, and Lewis could convey Midwest-speak with the best of them. Nowadays, Stephen King artfully turns the New English phrase, Karl Marlantes brings soldier-speak to life in Matterhorn, and Richard Price features the parlance of the urban street in many of his novels. 

In recent literature, Gregory David Roberts imbues his myriad characters in the semi-autobiographical novel, Shantaram with perfect pitch. Most notable is the character of Prabaker, a streetwise slum dweller of Bombay, who, with his wide smile and stark optimism, befriends and endears himself to the novel's protagonist, and, because Roberts writes dialogue so adroitly, to the reader as well. Here are Prabaker's first words by way of introduction.
 ‘Good mornings, great sirs!’ he greeted us. ‘Welcome in Bombay! You are wanting it cheap and excellent hotels, isn’t it?’
In the subsequent exchange it really isn't even necessary to denote who is speaking since the author distinguishes Prabaker so completely:
‘What I want to see right now,’ I said, ‘is a clean, cheap hotel room.’ 
‘Certainly, sir!’ Prabaker beamed. ‘I can take you to a cheap hotel, and a very cheap hotel, and a too much cheap hotel, and even such a cheap hotel that nobody in a right minds is ever staying there also.’ 
‘Okay, lead on, Prabaker. Let’s take a look.’
Great dialogue speaks to the reader, is true to the character, and makes for memorable story telling.