The user hasn't said anything about using Linux. Perhaps you should tell the user how to delete the font cache in Windows.
Thanks phred for pointing this out, I was probably misled because I remember having the same message on Linux only, where rebuilding the font cache solved the case.
A batch file for that purpose under Windows 10 is provided here (see "Method 2", run batch and reboot):
https://techcult.com/rebuild-font-cache-in-windows-10/I have just tested it on my machine and switched MB to font Yu Gothic: no error message issued, and the
only title in Japanese from my collection is displayed correctly.
But the display was already flawless on Windows before (Japanese + Latin, Cyrillic, and Greek).
Note: MB works as a charm with .otf and .ttf fonts on both Windows and Linux (my distro: Linux Mint 18.3 x32 with wine installed).