mate-font-viewer: 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/mate-font-viewer - from package: mate-control-center

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