干嘛怎么复杂，意思是一样的。

That means ''Happy Birthday to you'

"祝你生日快乐" means "Happy Birthday" And 'Wish you Happy Birthday' in Chinese is "希望你生日快樂"...It's a bit strange...

Happy(快乐) Birthday(生日) to(给) you(你)，祝你生日快乐。 just like American never say Wish you Happy birthday.

If you add "WO" or I the translation is "I wish you a happy Birthday" and then is sounds very good. you could add "WOMEN" and you get "We wish you a happy birthday" if you just want to say "HAPPY BIRTHDAY" my dictionary suggests "shengri kuaile !