debdiff: 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/debdiff - from package: devscripts

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

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