apertium-rertf: 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/apertium-rertf - from package: apertium

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

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