The main thing that might be a problem is the command list, which is all in Japanese. It's pretty straightforward once you figure out that yellow = light attack, green = medium attack, and blue = heavy attack, though. And without at least some katakana knowledge, Mission Mode is going to be pretty hopeless.
In the name of the Railgun, and of the Missile, and of the Holy BFG. Amen.
Mission mode and tutorial might be frustrating tho since the directions are in japanese. But I believe someone is making mission guide or is finished making it which reminds me....shouldnt it be stickyed?
All the important stuff is in English, it's just the missions that'll be a ***** if you don't have any Japanese knowledge. However, all the Mission requirements were translated when the PS2 version was released. So unless they added new mission, this old topic should help.