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
IslamQA, a popular Islamic website, generally discourages the celebration of birthdays as it is not a practice endorsed by Islamic teachings. They believe that birthdays have no religious significance and can sometimes lead to imitating non-Muslim customs.
allons celebre des anniversaires
les anniversaires de ma famille