celtenc: 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/celtenc - from package: celt

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

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