Roboto Mono Font – How to Download and Install

Basically what you want to do is use the range operator to limit the characters that your new grub font contains. If you don't use the range operator then you're going to get all the glyphs including the erroneous or incorrect box elements from your target font.

For example:

grub-mkfont -s 16 --range=0x0-0x7f -o /boot/grub/grubfont.pf2 font.tty

Will generate a font with only ASCII characters, anything your font doesn't have should decay gracefully to the default font so boxes and arrows should come from the default. Please see this website for further information:

http://grub.enbug.org/gfxterm

mbaitoff, I'm posting this as addition to your update, not as an answer

If user creates file named ~/.fonts.conf:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <match target="font">
        <test name="spacing" compare="eq">
            <const>mono</const>
        </test>
        <edit name="embolden" mode="assign">
            <bool>false</bool>
        </edit>
    </match>
</fontconfig>

then, applications can use bold monospaced font if available, and disable "synthetic boldification" if used font does not have bold typeface.

It is just alternative, and slightly different approach with different result