what to write in a spanish christmas card

It depends on who the card is for and the type of relationship you have with them. If you are writing to a close friend or family member, you could write something like "Feliz Navidad y un prospero año nuevo" (Merry Christmas and a prosperous New Year) or "Que tus deseos se hagan realidad" (May all your wishes come true). For a more formal card, you could write "Estoy deseando que tengas una feliz navidad y que el nuevo ano te traiga mucha salud, felicidad y alegria" (I am looking forward to you having a happy Christmas