langdrill: 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/langdrill - from package: langdrill

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

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