Linux doesn't have a "system font" unless you mean:
* the console font
* one of the various "fixed" fonts that come with X11
* any of the default X11 fonts
None of which are likely to be used as the default for title bars, menus, etc.
* the console font
* one of the various "fixed" fonts that come with X11
* any of the default X11 fonts
None of which are likely to be used as the default for title bars, menus, etc.
Graphical distros have a standard font in their UI.
Oh well. Something else to roll into systemd!