Great Expectations contains lots of representations of Southern English working-class dialect, from the Kent area of the "marshes" and from London. For example, in Chapter 1, the convict Provis speaks very differently from Pip's own genteel diction:
“You bring me, to-morrow morning early, that file and them wittles. You bring the lot to me, at that old Battery over yonder. You do it, and you never dare to say a word or dare to make a sign concerning your having seen such a person as me, or any person sumever, and you shall be let to live. You fail, or you go from my words in any partickler, no matter how small it is, and your heart and your liver shall be tore out, roasted and ate."
The author includes these instances of speech to make the reader feel immersed in the environment of the book, and also to delineate the difference between working-class and upper-class characters. Words in rural English dialect in Dickens novels are written phonetically, to show how the author understood those accents to sound. Dialogue in nonstandard English also incorporates grammatical errors meant to show a difference in speaking convention between these characters and wealthier ones. Here, for example, Provis says "tore out" instead of "torn out" when he is using the past tense.
Provis's speech and that of working-class Kent characters also contains lots of spelling differences to indicate changes in pronunciation - "wittles" for "victuals," "partickler" for "particular." These dialects in Dickens's novels contain many words that don't exist in standard English now, like "wittles." This word means "food and drink," and is an example of rural working-class diction as well as pronunciation. It's notable that Pip himself doesn't ever speak with this dialect, even when the narrator remembers events and conversations from his childhood. Because of his desire to better himself and his "great expectations," he communicates (as both the narrator and as a character) like the wealthy and educated people he wants to emulate.
As part of their education, Victorian children were often required to learn psalms, poems, and songs. In Chapter 15, Dickens employs the regional dialect of Kent to give a sense of realism to the end of Pip's otherwise "preposterously" silly and inadequate education. This education consists of Biddy teaching him everything she has successfully learned. One of these items is a "comic song" which she has "bought for a half-penny," transcribed in idiomatic Kent diction:
When I went to Lunnon town sirs,
Too rul loo rul
Too rul loo rul
Wasn’t I done very brown sirs,
Too rul loo rul
Too rul loo rul
This piece of doggerel is a Dickensian version of a Kent country song, in which a rural person gets scammed, or "done very brown," by the city-folk. The nonsense words "too rul loo rul" are probably regional representations of vocables, or sung sounds. The song is not meant to serve as a good example of English folk music; it's just placed here by Dickens for some local flavor.
Pip says directly after this that he didn't "question the merit" of the song, but that even as a child he thought there was an "excess" of "too rul." His lack of experience with culture outside the "little catalog" of things Biddy shows him is simply too small to make a value judgement at this point. He only becomes able to do so when he is further along the arc of his development in the novel. As his "expectations" become greater and he is more exposed to music and the arts, the things he found to be wonderful in his childhood sometimes lose their sparkle.
