The winter tyres regulations differ throughout Europe. What applies in Austria is not the same as in Belgium or France. Sometimes winter tyres are mandatory and sometimes they are only recommended. In Germany, there is a winter tyre law. You must change from summer to winter tyres when there is black ice, slush and packed snow, i.e. "winter weather conditions". Anyone in Germany caught with summer tyres in these weather conditions can expect a fine of 60 euros and one point on their driving licence.
Also, since January 2018, only tyres with the Alpine (or snowflake) symbol are considered adequate. You have probably already the small three-jagged mountain with the snowflake in the middle. Tyres with this symbol have been officially tested for their winter properties and are particularly efficient in snow or on black ice.