apertium-postchunk: 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-postchunk - from package: apertium

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

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