Thank you for the answer.
Before applying to NATS I tried Skyguide ( almost good...) then Geneve Apron control, but they do not recruit for the moment. However I met them (Apron control) and they assessed my English (I had and interview with an English "teacher").
The guy told me that that English level ICAO is about 4.
I think i can quickly improve it if needed, I just hope I can start the selection then see what happens.