debconf-show: 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/debconf-show - from package: debconf

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

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