mwenext: 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/mwenext - from package: mediawiki-extensions-base

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

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