Birthdays = Geburtstage
Birthday = Geburtstag Birthdays = Geburtstage
Impossible to say. Not all publish birthdays.
if i remember correctly, my German teacher said it is zum geburtstag viel gluck
hacemos cumpleaños
cumpleaños diferentes
les anniversaires (masc. noun)
生 [sheng] 日 [riˋ]
People say stuff to you
Not much as far as I have read
allons celebre des anniversaires
les anniversaires de ma famille
It depends on the family and their beliefs and traditions. I know someone from Vietnam and they do not celebrate birthdays, but they say they know some people that do, just like us.