pybabel-python3: 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/pybabel-python3 - from package: python3-babel

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

Error in other languages:
pybabel-python3: bevel nie gevind nie
pybabel-python3: comandă negăsită
pybabel-python3: comando não encontrado
pybabel-python3: commande introuvable
pybabel-python3: command not found
pybabel-python3: käsku ei ole
pybabel-python3: không tìm thấy lệnh
pybabel-python3: komanda nerasta
pybabel-python3: Kommando nicht gefunden.
pybabel-python3: kommandot finns inte
pybabel-python3: komut yok
pybabel-python3: nie znaleziono polecenia
pybabel-python3: níor aimsíodh an t-ordú
pybabel-python3: no se encontró la orden
pybabel-python3: no s'ha trobat l'ordre
pybabel-python3: opdracht niet gevonden
pybabel-python3: parancs nem található
pybabel-python3: perintah tidak ditemukan
pybabel-python3: príkaz nenájdený
pybabel-python3: příkaz nenalezen
pybabel-python3: команда не найдена
pybabel-python3: командата не е открита
pybabel-python3: 命令找不到
pybabel-python3: コマンドが見つかりません