Another expression we are often asked to translate into Japanese is "happy birthday". This page explains everything, whether you are writing it or saying it.
In Japanese, “happy birthday” is written (お) 誕生日 おめでとう (ございます). This is pronounced “(o) tanjoubi omedetou (gozaimasu)”.
If we break down this expression:
- “o” is the polite form
- “tanjobi” (たんじょうび) means "birthday"
- “omedeto” means "congratulations"
- “gozaimasu”, if you want to add that as well, it means “many”
So if you want to say happy birthday to a close Japanese friend, you can just say "tanjobi omedeto". But the full and more polite version would be "o tanjobi omedeto gozaimasu".
Young people are more and more likely to say ハッピーバースデー happy bazde to one another, which sounds like "happy birthday" in English.
To ask how old someone is you say 何歳ですか nan sai desu ka ?
For the record, birthdays have been celebrated in Japan since about 1950. Previously, all Japanese birthdays were celebrated over the new year!
Now the tradition is similar to that in the West and people have a cake with a candle and sing Happy Birthday (in English). For couples, a birthday is a romantic celebration, a bit like Christmas Eve.