The novel uses dialect in somewhat complex ways to signal characters' social class. For example, in Chapter 18, the Artful Dodger has to translate his own speech for Oliver:
"If you don’t take pocket-hankechers and watches," said the Dodger, reducing his conversation to the level of Oliver’s capacity, "some other cove will; so that the coves that lose ’em will be all the worse, and you’ll be all the worse too, and nobody half a ha’p’orth the better, except the chaps wot gets them—and you’ve just as good a right to them as they have."
The Dodger speaks English, but a version of it that he picked up as a poor young pickpocket in London. Even his translation to Oliver requires some parsing for most modern English speakers. Basically, he means that someone is going to steal rich people's pocket handkerchiefs and watches, so it might as well be Oliver and his new friends. Fagin calls the Dodger's short speech "the catechism of his trade." A catechism is a series of questions and answers that convey the central principles of Christianity, and Christian children are often taught to recite it as part of their religious education. Fagin's comment is a bit of a joke, but it suggests that the Dodger's speech patterns are emblematic of his indoctrination into thievery. The Dodger is Oliver's initial guide not only into a pauper's London, but more specifically into the criminal subculture of London. The fact that Oliver can't understand the Dodger at first when he refers to pocket handkerchiefs and watches as "fogles and tickers" reinforces that Oliver is not yet at home in this subculture.
Many characters who are not criminals speak in some sort of dialect. In general, the wealthier a character is, the closer their speech is to standard English. But a sort of dialect is also used to bolster the anti-Semitic depiction of Barney, one of Fagin's associates who is also Jewish. Barney's speech would not be considered a dialect by linguists, but Dickens uses creative spelling to emphasize that he speaks "through his nose"—he has particular difficulty pronouncing the letters s, m, and n. Dickens seems to be making an unsettling joke based on the stereotype that a Jewish person's nose is their defining feature. Like the Dodger, Barney's speech is emblematic of the class of person the novel supposes him to be.
