apertium-validate-acx: 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-acx - from package: apertium

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

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