Use an alternate font with GTK3 app Zenity

#!/bin/sh
MONOTEST="\n\n1. --- www [[[ ... %%%\n2. www [[[ %%% ... ---\n"

# Normal font
zenity --info --text="This is NOT monospace$MONOTEST"

# Alternate font
FONT="DejaVu Sans Mono"
exec 2<<-EOF
        <?xml version="1.0"?>
        <!DOCTYPE fontconfig SYSTEM "fonts.dtd">
        <fontconfig>
                <dir>/usr/local/share/fonts</dir>
                <dir>/usr/local/lib/X11/fonts</dir>
                <cachedir>/var/db/fontconfig</cachedir>
                <match target="pattern">
                        <edit name="family" mode="assign" binding="same">
                                <string>$FONT</string>
                        </edit>
                </match>
        </fontconfig>
EOF
FONTCONFIG_FILE=/dev/stderr \
        zenity --info --text="This is monospace$MONOTEST"