babel: 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 CentOS possible default full paths are:

/usr/bin/babel - from package: openbabel

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/babel - from package: openbabel

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

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