Umm... are you talking about SMBX or what? Do you want to change SMBX's language to Japanese? I'm sorry, but I simply have no idea what you're talking about!
Legacy SMBX itself is non-translatable. But you can make Japanese translation for PGE Editor and PGE Engine (alternate editor for SMBX levels and episodes and developing game engine which will success SMBX engine) which are translatable, and guide how to translate is here: http://wohlsoft.ru/pgewiki/Translating_ ... _languages