how do we say merry christmas in australia

Oh, that's a good question! In Australia, they say "Merry Christmas" just like in most English-speaking countries. However, there is one special greeting that is specific to Australia, and it's called "G'day mate!" It's a friendly way to greet someone, and it's used as a general greeting as well as a Christmas greeting. So you could say "G'day mate, Merry Christmas!" to a friend or family member in Australia!