In French there are TWO ways of saying WELCOME. The first way is to accept somebody which is 'BONJOUR!' The other way you say after someone told you thanks which is 'DE RIEN'.
il n'y a pas de quoi (from google translate)je vous en prie-formalje t'en prie-causalit won't turn out exactly as you're welcome in a translator, but it's used the same way