zsh5: 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:

/bin/zsh5 - from package: zsh

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

Error in other languages:
zsh5: bevel nie gevind nie
zsh5: comandă negăsită
zsh5: comando não encontrado
zsh5: commande introuvable
zsh5: command not found
zsh5: käsku ei ole
zsh5: không tìm thấy lệnh
zsh5: komanda nerasta
zsh5: Kommando nicht gefunden.
zsh5: kommandot finns inte
zsh5: komut yok
zsh5: nie znaleziono polecenia
zsh5: níor aimsíodh an t-ordú
zsh5: no se encontró la orden
zsh5: no s'ha trobat l'ordre
zsh5: opdracht niet gevonden
zsh5: parancs nem található
zsh5: perintah tidak ditemukan
zsh5: príkaz nenájdený
zsh5: příkaz nenalezen
zsh5: команда не найдена
zsh5: командата не е открита
zsh5: 命令找不到
zsh5: コマンドが見つかりません