Same for X9 and S9 Service Manuals. Japanese, with some limited English for certain words (mostly some universal EE terms).
It is really no handicap at all. Except for the parts lists the Service Manuals are useful for design/repair/information by people who have electronics background and experience. Those people can read schematics and EE flow charts. Those are universal, involve universal trade practices, and use a minimum of "language" of any kind. There is no descriptive text providing directions or guidance.
As to "rare?" Especially with the X0 - they were hard to get ten years ago, as the players were sold in relatively small quantities. While in production there was little consumer use for the Manuals. And once the models ceased production the ability to even access knowledge of their existence dropped off the radar. It took me almost a year to get mine; over 4 months once I paid for them.
BTW - if you ARE able to get an X0 Service Manual PLEASE let me and other Forum members know. I misplaced mine sometime in the past 4 years, and have left only my X9 and S9 versions.