I would not profess to be a "touring cyclist", but, I do cycle quite frequently in Europe (France, Spain, Germany, Luxembourg), since I use a bicycle as transport when my campervan is "parked up". I am not sure of the legal situation, but, my general observation is that the Brits are the most likely to wear helmets, for "casual" cycling, the rest of our European Cousins appear to wear them for on-road cycling with road bikes, but, otherwise (generally) not.