What freaks me out is ... correct me if I'm wrong ... is that the written language is identical? As if an american spelled "Bill Smith" was called "Bill Smith" in Michigan, but "Rear Ditch" in Texas
Written language is the same. Only difference is if it is written in local Cantonese or standard Chinese. Non Cantonese speakers reading Chinese written in local Cantonese would not make sense of it for local slang terms.