Answer by Professional Japanese Teacher
Tanjoobi omedetoo gozaimasu
Birthday is 誕生(たんじょう)日(び) tanjoobi in Japanese. おめでとうございます omedetoo gozaimasu literally means “congratulations”. This is a useful expression as we can use this for any congratulatory occasions, simply by adding it after the event.
For example, if we want to congratulate someone on getting married, we can say “ご結婚(けっこん)おめでとうございます gokekkon omedetoo gozaimasu”, with ご結婚(けっこん) gokekkon being “marriage or wedding”. To congratulate someone on his graduation, we can say 卒業(そつぎょう)おめでとうございます sotsugyoo omedetoo gozaimasu.
I’m sure your friend would be happy to receive your birthday message.