The fixme is for the pango case, which should work, despite the fixme.
what probably doesn't work is make_xfont_monospace.

Are you using zvt or vte, and with core X fonts, Xft1, or Xft2?

I'm using libzvt of libzvt-i18n with gnome-terminal
from gnome-2-0 branch + a patch to enable pango 
font for libzvt case. libzvt-i18n converts 
PangoFontDescripion to X11 fonts, though.

make_font_monospace(term->style->font_desc) always
return NULL, and then it goes into
 desc = pango_font_description_copy (terminal_profile_get_font (profile));

Does it mean it always use terminal's font setting , and ignore
system's settings?

You'll probably need to dive into pango a bit and see why 
there's no font which is like the system font but called "monospace"...

Of course, with the Font control panel containing a terminal font 
now, it's unclear we still need the "use system font" option.

But, will you please answer why return NULL
below?

In src/terminal-screen.c:

make_font_monospace (const PangoFontDescription *font)
{
  PangoFontDescription *ret;

  return NULL;     <=== ??

  ret = pango_font_description_copy (font);

  /* FIXME */
  pango_font_description_set_family (ret, "monospace");

  return ret;
}

gnome-terminal starts repsonding to "use system font" after removing
this return NULL line.

Is this change okay to commit to both branches?

Oh, no clue. I didn't notice that. ;-)

Yes, please commit. Though on HEAD I think we may just nuke this setting 
eventually, it may as well work while it's there.

commit to both branches. Thanks!

	* src/terminal-screen.c (make_font_monospace):
	  Fix #96114: to responce to "use system font" option