I am using FOP 0.15 Version. The PDF files rendered by FOP gives junk charecters for double-byte languages like korea, japan etc.
FOP 0.15 doesn't support non-latin scripts properly. Your only chance is to upgrade to FOP 0.19 or later, preferably the latest release, 0.20.5. This also means that you have to rewrite parts of your FO generator because of incompatible changes in the spec (drafts) implemented by FOP.