Do you consider that it should be allowed by law to have one day off per month - without needing medical leave - for all those women who have very strong menstrual pains?

You're asking some tough questions I may well agree with that but some people would abuse the system so I'd say no...keep it as it is. You go off sick for any reason you adhere to your companies sickness policy...although I do have sympathy for the period issue it's just not feasible and would cost hundreds of millions in lost work days.