There are many psytrance festivals in France, the most famous one are:
Hadra Trance Festival France
Son Libre Festival France
Ethereal Decibel Festival France aka EDC Festival
People are strange France
Nataraja Festival France
Okami Festival France
Chateau Perche Festival France

in past there were festivals like
Stone Moon Festival France
Ambiosonic Festival France

You can discover all psytrance festivals in France via this page