The Pickwick Papers/WMG

Mr.Jingle suffers from some bizarre form of aphasia

That's why he's such a Strange Syntax Speaker. The only reason Job Trotter can understand and translate for him is because they know each other enough, and it's outright stated that Mr. Pickwick only understands him because of his knowledge of shorthand writing. There are also a handful of times where it would have benefited Jingle to speak plainly, suggesting that he isn't able to simply drop his speech mannerisms whenever they become inconvenient.