From Sandman:
It seems Nekomamushi's distinct speech pattern (Tosa dialect) is missing in their translations... Considering the dialect and his line "the man who awaits the dawn of this world", Nekomamushi is probably based on Ryoma Sakamoto, one of the most famous patriots in Japan.
For reference, below are some characters who have distinct speech patterns.
Akainu: Hiroshima dialect
Hiroshima was famous for yakuzas several decades ago. According to Oda, Akainu is based on Bunta Sugawara, who starred in many yakuza film.
Bartolomeo: North Kanto/Tohoku/Hokkaido dialect
Considering his vulgar behavior, he is probably based on the famous bad boys who live in North Kanto district.
Kaku: Old man speech style
Duval: (Probably) Tohoku dialect
Tontatta: lisping