apertium-validate-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-validate-postchunk - from package: apertium

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

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