Okay, bare with me here.
Searched: various groupings of speech therapy, speech pathology, lisp, speech-language therapy/pathology with eastern asia and china. Through these, I discovered a few resources for SLP on the eastern seaboard of China and throughout major cities in Eastern Asia, and an article written by a speech therapist working in Central China.
Scenario: So, I have this post-apocalyptic Zodiac story I'm working on. China has taken over the vast majority of Asia, and several other locales around the globe. The story follows the twelve characters that embody each of the Chinese Zodiac signs. Two of the characters--Ji and Tu--are both of mixed blood, which is considered a great dishonor in the new world order (Ji's father killed himself when he found out Ji's mother was pregnant; Tu's parents were both already slaves, and Tu was adopted by their master and groomed to become the master of the house). Here is where the scenario's divert: Ji, being raised as sort of a street urchin and around prostitutes his whole life speaks, for the most part, in heavy slang. Tu, at the age of 12, is still suffering from what in English would be considered a lisp.
Obviously, because I speak English (well, American anyway), the story is going to be in English. These questions are to try and figure out the appropriateness of the situation.
1) Is there a Chinese equivalent of a lisp? This is not attributed to a cleft lip or pallet (which, as I understand, can cause major issues with speech), but a simple displacement of the tongue during regular speech (dental lisp) as well as some misfiring in different speech sounds (glottal lisp; my terms may be off, it's been a while since I stopped attending speech therapy for my own lisp). I suppose what I mean, with this question, is are there people who lisp in Chinese in a fashion that is comparable to an English lisp ("th" noises instead of "s", and sometimes "sh" noises instead of "f")?
2) What resources would be available to correct a lisp/speech "issue"? Tu lives in an affluent area and is raised by a very powerful man, so assume that any resources would be available. Are there speech pathologists in China that would work with a lisping child (if, in fact, question 1 is answered with "Yes, China does have lisps")?
3) In the case of Ji, is there a large discrepancy of slang to affluent dialog in the Chinese language? I know about Mandarin and Cantonese and all that, but are there subset dialects to the distinct dialects that would be considered a "slang language" (ie, Southern as compared to Midwestern, or, better yet, Cockney rhyming slang as compared to "The Queen's English")?
ETA: Thanks everybody! All the information has been really helpful (and I'm sure me taking Chinese in college will also help on this matter), and I think I'm ready to start flushing practice dialogue for both characters, just so I can get a handle on how they talk. All the info has been great!