10 Popular Chinese Mid-Autumn Festival Greetings/Sayings
Mid-Autumn Festival!
Happy Mid-Autumn Festival! 快乐! Zhōngqiū kuàilè!
Wish you and your family a happy Mid-Autumn Festival 祝你和你的家人中秋快乐 Zhù nǐ hé nǐ de jiārén zhōngqiū kuàilè

Wishing us a long life to share the graceful moonlight, though thousands of miles apart.但愿人长久，千里共婵娟  Dàn yuàn rén chángjiǔ, qiānlǐ gòng chánjuān

A bright moon and stars twinkle and shine. Wishing you a merry Mid-Autumn Festival, bliss, and happiness.皓月闪烁，星光闪耀，中秋佳节，美满快乐！
Hàoyuè shǎnshuò, xīngguāng shǎnyào, zhōngqiū jiājié, měimǎn kuàilè!

Happy Mid-Autumn Festival! May the round moon bring you a happy family and a successful future.祝福中秋佳节快乐，月圆人圆事事圆满. 

The roundest moon can be seen in the autumn. It is time for reunions. I wish you a happy Mid-Autumn Day and a wonderful life.月到是秋分外明，又是一年团圆日，祝你节日愉快，身体安康

Source: https://www.chinahighlights.com/festivals/mid-autumn-festival-greeting.htm