The font of the menu of a package on Debian 9 Xfce doesn't look fine

For the package GeoGebra 5, the text of the menu bar looks bad, with a strange (and unwanted) font. This is the normal, good look of the menus of other programs: This behavior is new. It's happening since around one week ago. Before this issue, I was tired by a poor appearance of my desktop: it looked with an old-fashion; almost all the fonts of the desktop looked no so well. So, I followed this suggestion: https://forum.manjaro.org/t/better-font-settings-in-easy-way-xfce-and-gnome/24319 However, I didn't make the step for Qt configuration. My system works with Qt4. Maybe this is the reason for the trouble. Today, I tried with the Qt4 configuration, font substitution. However, I don't know how to manage rightly this setting. I guess that the shown font is Abydos (it appears in the Qt4 font setting window, substitution area; it's exactly the first item in my fonts list). I have tried too: - changing some options in Setting tools Appearance and Windows Manager - uninstalling (https://askubuntu.com/questions/151941/how-can-you-completely-remove-a-package , post of user2777677), deleting the geogebra and GeoGebra folders of my .config directory, and reinstalling GeoGebra 5 without fixing the issue. My system: Debian 9, Xfce, 64 bits This questions could be similar to my case: - https://unix.stackexchange.com/questions/126281/weird-bug-with-xfce4-menu-panel-font-very-small - https://unix.stackexchange.com/questions/443065/fix-for-ugly-fonts-in-programs-like-keepassxc-or-nextcloud-on-antergos-with-gnom