Then WHY would it be in English, since in Japan they all speak and read Japanese? Of course Suikoden is in Japanese, even the very first menu screen.
I never, ever, heard of ANY Japan-only RPG that actually had all of it's main texts in English. That only happens to action games, that require little to no reading, like shooters. In Japan they find that menus looks cool in English and stuff, but it stops there.