Rules do differ from one country to another. You need to find out what the LAW says about flying RC in France.

Some countries can be very loose in their laws about RC... others can be very strict. In the US... if not trying to obey the AMA safety code... as long as you don't militarize the model its probably legal. All you need is pernmission from the site owner to be allowed to fly at any location. (though... permission to fly somewhere does not mean its a good place to fly a particlular model.)

Though its not smart... and could lead to a huge lawsuit if you cause damage or hurt someone, its LEGAL in the US to launch a model rocket from an RC airplane.

The rules about operating the radios vary mainly in what frequencies are allowed. (mostly 72 mhz in the US... I think its 35 or 45 mhz in England. No idea what band in France.)