Gōnɡxǐ xīnhūn.
恭喜新婚.
Congratulations on your wedding.
Notes:
恭喜(gōnɡxǐ): congratulation
新(xīn): new
婚(hūn): marriage
Example:
A: 恭喜新婚 。
Gōnɡxǐ xīnhūn.
Congratulations on your wedding.
B: 谢谢。
Xièxie.
Thank you.
