Dydd Santes Dwynwen is the all Welsh lovers celebrate, rather like the English St Valentine(in Latin, Valentinus) who was is a widely recognised third-century Roman saint commemorated on February 14 and associated since the High Middle Ages with a tradition of courtly love.
Nothing is reliably known of St. Valentine except his name and the fact that he died on February 14 on Via Flaminia in the north of Rome. It is uncertain whether St. Valentine is to be identified as one saint or two saints of the same name. Several different martyrologies have been added to later hagiographies that are unreliable. For these reasons this liturgical commemoration was not kept in the Catholic calendar of saints for universal liturgical veneration as revised in 1969, although he continues to be honoured on February 14th in the extraordinary-form Roman calendar of saints.
In this case, St Dwynwen seems to have the truer story, and she's made in Wales - not like the obscure foreign saints that the English worship!