haha i realise that it sounds like it's a good idea to major in stuff you think you want to study, but when you get to uni it's a whole different matter. 2 majors in commerce sound good and stuff, but that's hard enough as it is. sweetie even in a 5 year course you wouldn't want to do 4 majors. have you really explored what are the criterias for completing a major? you should really go and have a look at which 2 commerce majors you want to do, and the units you have to do to complete it.. and same goes for japanese and especially psychology.
i'm doing comm lib now, and i'm doing japanese as a 3rd major and i did a unit from psyc and not planning to do anymore. i have heard that you can't do psychology as a 3rd major because you don't have enough credit points. if you want to do a japanese major i don't see how you will be able to do more psychology than psyc 1a and 1b.
anyway the good thing about comm lib is that you do have a bit of room to explore what you want to do in the first year.. but if you want to do 3 majors etc, than you need to plan out your course and by the sounds of it you're not really quite sure what you learn in psychology. but just a hint, you don't actually get to tell what's wrong with people or become the master of manipulation.