How does language work in the trial scene in To Kill a Mockingbird?

The trial scene is probably one of the most memorable in Lee's novel.
In the scene, Lee uses language to highlight the main conflict of the story: convention versus truth. Convention has it that all black men are predisposed towards acts of violence against white women. Depending on one's personal convictions, the opposite may sound just as plausible: all white men are predisposed towards acts of violence against black women. Of course, neither of these statements are intrinsically true. They are just based on differing biases.
It isn't the race of the man that determines his actions but his worldview. Lee demonstrates this perfectly in the trial scene. She uses language to expose the entrenched racism of Bob Ewell and those who support him. Alternatively, Atticus Finch's studied diction and dignified demeanor speaks volumes about the depth of his character. Lee juxtaposes Bob Ewell's colloquial, inflammatory diction against Atticus' clear, concise speech to show that two worldviews are at war in the courtroom.
One worldview champions racist, intolerant views, while the other advocates egalitarian ideals. Here is an exchange that involves Atticus and Bob Ewell:

"I'll repeat the question," said Atticus. "Can you read and write?"
"I most positively can."
"Will you write your name and show us?"
"I most positively will. How do you think I sign my relief checks?" . . .
"What’s so interestin'?" he asked.
"You're left-handed, Mr. Ewell," said Judge Taylor. Mr. Ewell turned angrily to the judge and said he didn't see what his being left-handed had to do with it, that he was a Christ-fearing man and Atticus Finch was taking advantage of him. Tricking lawyers like Atticus Finch took advantage of him all the time with their tricking ways. . . .
Mr. Gilmer asked him one more question. "About your writing with your left hand, are you ambidextrous, Mr. Ewell?"
"I most positively am not, I can use one hand good as the other. One hand good as the other," he added, glaring at the defense table.

Bob Ewell's ignorance is apparent to all. Here, it's obvious that he doesn't understand what the word "ambidextrous" means. Yet, this doesn't stop him from accusing Atticus of being a "tricking" lawyer. Ewell also refers to himself as a "Christ-fearing man," no doubt appealing to religious Southern sensibilities. So, language is especially important in the trial scene. It reveals the character of the person speaking. Bob Ewell uses witticisms to endear himself to the crowd and then switches to accusatory proclamations to defend himself against perceived attacks.
Mayella's language mirrors that of her father, Bob Ewell. Her fear during cross-questioning is palpable, and like her father, Mayella uses inflammatory accusations as a defense mechanism:

"What are you scared of?"
Mayella said something behind her hands. "What was that?" asked the judge.
"Him," she sobbed, pointing at Atticus.
"Mr. Finch?"
She nodded vigorously, saying, "Don’t want him doin' me like he done Papa, tryin' to make him out lefthanded..." . . .
"Won't answer a word you say long as you keep on mockin' me," she said.
"Ma'am?" asked Atticus, startled.
"Long's you keep on makin' fun o'me."
Judge Taylor said, "Mr. Finch is not making fun of you. What's the matter with you?"
Mayella looked from under lowered eyelids at Atticus, but she said to the judge: "Long's he keeps on callin' me ma'am an sayin' Miss Mayella. I don't hafta take his sass, I ain't called upon to take it." . . .
"Who beat you up? Tom Robinson or your father?" No answer.
"What did your father see in the window, the crime of rape or the best defense to it? Why don't you tell the truth, child, didn't Bob Ewell beat you up?"

Both Mayella and Bob Ewell are hiding an uncomfortable truth: Tom may not have been responsible for Mayella's injuries. The text hints that Bob is Mayella's likely abuser. Mayella's emotional language betrays her fear that the exposure of the truth could jeopardize her own safety at home.
As for Tom, his language is respectful and precise, despite his colloquial diction. He gives clear answers to every question he is asked.
To recap, Harper Lee uses language to highlight the conflict between two opposing worldviews in the courtroom. By extension, she exposes the destructive philosophical dichotomy at play in the South in the 1930s.