Dialect is a group’s special way of speaking, and sometimes when authors attempt to capture dialect in their writing it comes out hard to understand, especially if the reader is unfamiliar with it.
Chances are if you are reading Great Expectations, the way people are speaking seems different than the way you are used to hearing them speak. This is because as the reader, you are from a different time and place than the characters. Dickens uses dialect to help the characters come to life by writing the way they speak.
An example of dialect early in the book is Magwitch’s language. Magwitch is poor, and speaks like a poor person. This is why his words can be sometimes hard to understand.
“Ha!” he muttered then, considering. “Who d'ye live with—supposin' you're kindly let to live, which I han't made up my mind about?” (ch 1)
What he actually said was: Ha! Who do you live with—if you are kindly allowed to live by me, which I have not made up my mind about?
Sometimes it helps to read the dialect out loud or listen to an audiobook version of someone reading the story. Then you can sit back and enjoy the conversation, rather than trying to translate it.