deluser: 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/sbin/deluser - from package: adduser

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

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