Thank you everyone
Thank you to everyone for your pieces of advice and all the information you give.
I understood : be myself, that is to say, be a team player. No trainers but street shoes. No jeans but trousers. Tie is not necessary. No chewing gum. Ok, that's all me ! So I shouldn't be worried out of that.
To answer to Ciccio78, I had a invitation 11 days after I sent my application form.
Thank you for your help and your support. I'll have to manage with it anyway.