My solution is too simple. I examined /var/log/Xorg.0.log
and found the following:
[ 52.308] (WW) The directory "/usr/share/fonts/X11/cyrillic" does not exist. [ 52.308] Entry deleted from font path. [ 52.308] (WW) The directory "/usr/share/fonts/X11/100dpi/" does not exist. [ 52.308] Entry deleted from font path. ... [ 52.314] (WW) The directory "/usr/share/fonts/X11/75dpi" does not exist. [ 52.314] Entry deleted from font path. [ 52.314] (WW) The directory "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType" does not exist. [ 52.314] Entry deleted from font path.
So, I installed the indicated packages:
xfonts-100dpi xfonts-cyrillic ... defoma psfontmgr x-ttcidfont-conf
I rebotted and Dotty graphs became beautiful, but the default font name remains unknown for me.