If I remember correctly, the accent system was devised by the english translation team, in order to do less work(IE writing most of the lines only once, as opposed to writing lines specifically for all 50 characters). Also if I remember correctly, Kid spoke with a Kansai dialect in the original. Kansai being a somewhat slang style of japanese... sort of disrespectful or unrefined in certain areas of Japan, but considered the norm in others. Another note about Kansai is that, when directly translated, the sentences typically line up fairly close to traditional Japanese, meaning that they had to take liberties with the english dialog in order to show that Kid spoke differently.
Note, that some of my explanation may be incorrect, as I speak very very little Japanese, and I read the information about Jp Chrono Cross a significant while ago.....
On the topic of accents and where they come from, where exactly would Korcha obtain his, uhh.... "unique" accent? (Ok screw it, its bad... terrible, horrible, like his hair... his weapon, his pantslessness and everything else about him... I despise KorCHA with a paCHAn... O.<; )
