What is 'Happy St Joseph's Day' when translated from English to Italian?

If you are speaking directly TO someone named Joseph and want to wish THAT person a Happy St. Joseph's Day, you would say "Buon onomastico", which is "happy feast day". This would be true of anyone on their "name" or feast day. To say to someone else "Happy St. Joseph's Day" one would say "Buona Festa di San Giuseppe", which is more literally, happy Feast of St. Joseph.