How do you say seventieth anniversary in Latin?

Felix natalis quinquagesimus

next time you can always go to google translate =)

It would actually be Felicem Quinquagesimum Natalem Diem, because it is being said and would therefore be in the accusative case, with the implied "habe."

google Translate isn't really all that good; don't use it. It can seriously mess up grammar when translating.