In Windows 10, NVIDIA 650Ti graphics card with updated drivers, all menu and message characters from gnucash 3.1 displayed as boxes. Numbers and account names displayed fine. Upgraded to current 3.3, and the same problem occurs. I can read the account data, but the menus and messages show up as boxes. I recently upgraded from Windows 7 to Windows 10. Everything worked fine under Windows 7, not under Windows 10.
What are your Settings>Language and Region settings? Do any of AppData\Local\gtk-3.0\gtk.css, AppData\Local\gtk-3.0\settings.ini, or AppData\Roaming\GnuCash\gtk-3.0.css exist in your home directory? If you create a new user, log in as that user, and start GnuCash are the menus readable?