pip3: 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/pip3 - from package: python3-pip

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

Error in other languages:
pip3: bevel nie gevind nie
pip3: comandă negăsită
pip3: comando não encontrado
pip3: commande introuvable
pip3: command not found
pip3: käsku ei ole
pip3: không tìm thấy lệnh
pip3: komanda nerasta
pip3: Kommando nicht gefunden.
pip3: kommandot finns inte
pip3: komut yok
pip3: nie znaleziono polecenia
pip3: níor aimsíodh an t-ordú
pip3: no se encontró la orden
pip3: no s'ha trobat l'ordre
pip3: opdracht niet gevonden
pip3: parancs nem található
pip3: perintah tidak ditemukan
pip3: príkaz nenájdený
pip3: příkaz nenalezen
pip3: команда не найдена
pip3: командата не е открита
pip3: 命令找不到
pip3: コマンドが見つかりません