The lilac genus consists of about 30 species that originally grew in Asia Minor and South-Eastern Europe. Most species can tolerate temperatures to -40 degrees Celsius that indicates that the originally wild flora of the species came from areas where it could become exceptionally cold.
In short, lilacs are extremely winter hardy. The Syringa Vulgaris species and its varieties require a minimum number of cold hours to activate the flowering process and that means that they will not grow as well or at all in warmer regions! But you can confidently plant it in the North of Lapland or Northern Spain. The Josée and Pink Perfume varieties will even flower abundantly in the most southern point of Spain.