mtbl_dump: command not found

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/mtbl_dump - from package: mtbl-bin

You may install the required package with command apt-get install {package}

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