“Happy birthday!”:

• shēng  rì  kuài  lè!（生日快乐！）

“Happy birthday to you!”:

• zhù  nǐ  shēng  rì  kuài  lè!（祝你生日快乐！）
  
  

Sometimes people make fun of close friends by replacing the first character, zhù (祝, wish), with zhū (猪, pig), so the sentence becomes:

“Happy birthday to you, pig!”:

• zhū  nǐ  shēng  rì  kuài  lè!（猪你生日快乐！）

Happy birthday to myself

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