Most likely the english voices are due to that it was released first for NA and Japan was the last one to receive the game. heh, even though it was developed by Sega Japan.
Signature
Handheld: NDS Lite (v7) with FlashMe v8a (to remove the Nag Screen) Flashcard: SCDSTWO (1.4.1 compatible firmware) w/ EOS 1.07