when we say "Happy ****"in English, we translate "**** happy"in chinese according to its meaning.
eg. "Happy SANKRANTI", "happy"=快kuai4乐le4
SANKRANTI 快乐 or SANKRANTI 节快乐。 or “桑sang1格ge2拉la1提ti2”节快乐。
节jie2=holiday
eg. "Happy New Year" New Year=新xin1 年nian2
“新年快乐”
eg."Merry Christmas" Merry=Happy Christmas=圣诞or圣诞节sheng4 dan4 jie2
圣诞节快乐! or 圣诞快乐!