mumble: 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 - from package: mumble

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

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