update-language: 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/sbin/update-language - from package: tex-common

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

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