My wife is Vietnamese, her mother is from Vietnam. I bought my mother-in-law a Christmas present and I want to write on the card "Merry Christmas (proper Vietnamese appellation)!" What should I write?

Dear Mr. and Mrs...

Thank you very much for welcoming me to your home again.

Merry Christmas!

From...

I know a woman who speaks almost no English. I want to give her a Christmas card and include a message in Vietnamese that she will understand. Where can I go to be able to copy Merry Christmas and maybe God bless you?
I am surprised to see this greeting in English style characters but that is perhaps for speaking. I am thinking of Asian characters, and I wanted to be able to copy them down on a card.