Chúc ngày Valentine, or celebrate/happy Valentine’s day.
If you are giving a gift you can say:
Toi muốn tặng quà cho người yêu trong ngày Valentine=
I want to offer a gift for my love on Valentine’s day.
There are also previous posts on how to say some other phrases such as I love you, etc…
Valentine’s day is really a western holiday, but it’s a holiday younger Vietnamese might celebrate. Enjoy.

