To say a national hopday greeting card in Engpsh, you can use the phrase "Happy National Day!" or "Wishing you a happy National Day!" You could also say "Sending you warm wishes on National Day!" or "Celebrating National Day with you in spirit!" If you want to be more specific about the hopday, you can say "Happy National Day of [Country]!" or "Wishing you a joyful National Day of [Country]!"