I forgot to mention the nice Tk module called Tk::FontDialog. It allows you to recursively go thru widgets and change fonts. It is used something like this:

use Tk::FontDialog;

my $fd = $mw->FontDialog(
        -nicefont => 0,
        -title => 'Select Font',
        -applycmd => \&apply_font,
        -fixedfontsbutton => 1,
        -nicefontsbutton  => 1,
    );

sub apply_font {
  my $font = shift;
   if ( defined $font ) {
      $rotext->configure( -font => $font );
      $mw->RefontTree( -font => $font );
      $top->RefontTree( -font => $font );
    }
}
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