This is actually really simple. Just mix together some phrases. The phrases are fixed phrases, and so using a computer translation system will ruin the card.
Key phrases:
- To Yuki, I/We wish you and yours (for person + family)
- Dear Yuki, Wishing you
- a (very) Merry Christmas
- Happy/Wonderful/Fantastic New Year
- Happy/Wonderful/Fantastic 2018
- Have a very Merry Christmas and a Happy New Year
- Wishing you all the best these holidays
- Peace, joy, and love to you and your family.
- May your Christmas season be filled with joy
- Sending you happy tidings this holiday season.
- May this New Year be filled with joy!
- God bless you this holiday season — Merry Christmas!
For more, see: https://holidappy.com/greeting-cards/Christmas-Card-Messages-What-to-Write-in-a-Christmas-Card.
DO: Use phrases nicely put together, and maybe add a personal message if you like. Messages in cards are usually short and simple. However, each message should be unique. Example:
Dear Yukihiro,
Wishing you a very Merry Christmas, and a wonderful 2018.
Many happy returns,
Hiroyuki & family
Another example:
To Masahiro,
We wish you a Merry Christmas and fantastic New Year. We hope all will go well for your trip to Vietnam this Spring.
Very best,
Hiromasa & Yuki