Hello Stefan,
You might, for instance, do something like this :
MENU ATTRIBUTE(STYLE="foo")
COMMAND "exit"
EXIT MENU
END MENU
and in your .4st style file :
<Style name=".foo">
<StyleAttribute name="fontFamily" value="monospace" />
<StyleAttribute name="fontSize" value="18pt" />
</Style>
Normally it should work. I invite you to consult the FGL documentation in order to get more details about the use of fonts :
https://4js.com/online_documentation/fjs-fgl-2.11.01-manual-html/User/PresentationStyles.html#USING_FONTS.
I hope it helps,
Best regards,
Lionel