" kuai　le sheng　rih ni " is Romanization of Simplified Chinese (SC). If u want to learn Chinese, u should learn Simplified Chinese (SC) or Tongyong Pinyin (TP) first. And " kuai　le sheng　rih ni " is an incorrect grammer in Chinese. The correct use is " zhu4 ni3 sheng rih4 kuai4 le4 (祝你生日快乐)"

i think you just tranlated happy birthday one by one: kuaile=happy, shengri=birthday, ni=you but chinese structure is: wish you birthday happy 祝你生日快乐 zhu ni shengri kuaile. or just birthday happy! 生日快乐 shengri kuaile!

e i think you wanna say "zhu ni sheng ri kuai le it means"happu birthday to you "

yep, it should be "zhu ni sheng ri kuai le" and that means "happy birthday to you"