Can you try a slight patch which I think would be better (i.e., not everyone uses Japanese) to see if it fixes the problem with Kanji filenames on Windows for you?
QString lang = QLocale::languageToString(QLocale::system().language());
Unfortunately, I don't have either Windows or a Japanese system to see if this works. My guess is that this will solve your problem by getting the system locale from Qt.
Thanks and best regards,