The reference to this file in the ReadMe for the PowerBook 5300 and 2300 series computers is in error. As of this writing, only the PowerBook 190 series computers require the Font Extension 3 file if Japanese Language Kit 1.2 is being used. On the PowerBook 190 series computers, the file can be found in the Apple Extras folder as referenced in the ReadMe.
The PowerBook 5300 and 2300 series computers do not require the Font Extension 3 file and the reference in the ReadMe should be ignored.