"Le auguro un felice compleanno." (I wish you a happy birthday — using the formal 'Le'.) . : "Auguri in ritardo!" (Happy belated birthday!) . Creative Birthday Cards
"Che questo giorno ti porti amore, felicità e tante sorprese!" (May this day bring you love, happiness, and many surprises!) :
Depending on who you are writing to, you can use these templates from sources like Preply and The Intrepid Guide: :
WeChat
Weibo