as uma thurman as "the bride" travels to okinawa and enters a sushi bar, the cook talks to his pal in proper standard-japanese, but in okinawa a quite different language, called 'ryukyuan', is spoken, although it's in japan.
If you read the Trivia at the Internet Movie Database (imdb.com) it points out that Okinawa is generally accepted as one of the worst places to get good sushi, making it an ideal place to go undercover by posing as a sushi chef. Hattori Hanzo and his assistant were not from Okinawa, but later moved there to hide out once Hanzo stopped making katana.
Actually standard Japanese is pretty much spoken all over Okinawa now. And the native laguage isn't "Ryukyun language" its Hogen which very few Okinawans still speak.
In most of Okinawa a dialect of Standard Japanese, which can be called Okinawa-ben, is spoken most of the time. Some of the older generation speaks Uchinaguchi, which means Okinawan Language in Uchinaguchi, but everyone knows Standard Japanese. There is a huge difference between Uchinaguchi, a seperate language from Japanese, and Okinawa-ben, a dialect of Standard Japanese. A comparison: Standard Japanese:Okinawa-ben::US Broadcasting English:Deep South dialect of English and Uchinaguchi:Standard Japanese::English:German
Hope that clears things up a bit.