I am unable to compare files with chinese filenames (binary/text/folder). They appear as ????.??? in the dialog box. I reckon it is the same for japanese filenames as well. I am using winXP professional.
I don't know if UltraCompare v4.20 supports Unicode filenames, I'm also only a user. I can see with a Total Commander plugin that most Windows kernel functions used by UltraCompare reference only to the ANSI version and the Wide (= Unicode) version is not used by UC. For some functions both versions of the function are referenced by UC. So it could be possible that UC does not fully support Unicode filenames.