airdecloak-ng: 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/airdecloak-ng - from package: aircrack-ng

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

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