mumble-server-cli: 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/mumble-server-cli - from package: python-django-mumble

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

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