grub-mkfont: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/grub-mkfont - from package: grub-common

You may install the required package with command apt-get install {package}
Error in other languages:
grub-mkfont: bevel nie gevind nie
grub-mkfont: comandă negăsită
grub-mkfont: comando não encontrado
grub-mkfont: commande introuvable
grub-mkfont: command not found
grub-mkfont: käsku ei ole
grub-mkfont: không tìm thấy lệnh
grub-mkfont: komanda nerasta
grub-mkfont: Kommando nicht gefunden.
grub-mkfont: kommandot finns inte
grub-mkfont: komut yok
grub-mkfont: nie znaleziono polecenia
grub-mkfont: níor aimsíodh an t-ordú
grub-mkfont: no se encontró la orden
grub-mkfont: no s'ha trobat l'ordre
grub-mkfont: opdracht niet gevonden
grub-mkfont: parancs nem található
grub-mkfont: perintah tidak ditemukan
grub-mkfont: príkaz nenájdený
grub-mkfont: příkaz nenalezen
grub-mkfont: команда не найдена
grub-mkfont: командата не е открита
grub-mkfont: 命令找不到
grub-mkfont: コマンドが見つかりません