AFAIK, ide is written in .net and this the main menu, so it will use the default font from Win Os system.
Maybe some special font is used in ide, which is missing from your system font folder.
Remove the IDE related .ini file after uninstalling? then reinstall.
For my case the B4J ini file is "C:/user/name/appdata/roaming/anywhere software/b4xV5.ini"
- Not tested.