mewest: 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/mewest - from package: mew-beta-bin
/usr/bin/mewest - from package: mew-bin

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

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