Merry Christmas is a common holiday greeting in English-speaking countries, but there are many different ways to express it in other languages. Here are a few examples in different languages:
French: Joyeux Noël!
Spanish: Feliz Navidad!
German: Frohe Weihnachten!
Italian: Buon Natale!
Russian: С Рождеством Христовым! (S Rozhdestvom Khristovym!)
Chinese: 圣诞快乐!(Shèngdàn kuàilè!)
Hope that helps!