The most common phrase is "Merry Christmas" but if you're looking to get a little more creative, you could also say "Joyeux NoeI" (French), "Buon Natale" (Italian), "Frohe Weihnachten" (German), "Feliz Navidad" (Spanish), "Shinnen omedetou" (Japanese), "Mele Kalikimaka" (Hawaiian), or "Mele Kalikimaka" (Hawaiian). There are many other options too!