I also had this problem. (before I got applocale) If you don't have it there is an alternate method that *should* work. It did for me but I don't know how other computers will take it.
Make a copy of that japanese named file somewhere else. I do this because the copy will be imported, there is a reason too. Next, in edit disk, right click the japanese one in the game, choose shell menu, then properties. Copy the name of the file in the text box here, which has no japanese characters, just random stuff, and then to the copy of the japanese file, rename it (you don't need right clicked properties here) to what you just copied. Then you should be able to import it.
I only have you rename a copy so as not to lose the japanese characters on the original.
Just posting this for anyone without applocale.
