Greeting with appropriate words is important for socializing. Here are some useful expressions for special occasions. Try sound files to help with your pronunciation.
Celebration
Omedetou gozaimasu.
おめでとうございます。
Omedetou. (casual)
おめでとう。
The form "gozaimasu (ございます)" is more polite. It is added when you are talking with somebody who is not a family members or a close friend. To reply, "Arigatou gozaimasu (ありがとうございます)" or "Arigatou (ありがとう)" is used.
O-tanjoubi omedetou gozaimasu. (formal)
お誕生日おめでとうございます。
Tanjoubi omedetou. (casual)
誕生日おめでとう。
Go-kekkon omedetou gozaimasu. (formal)
ご結婚おめでとうございます。
Kekkon omedetou. (casual)
結婚おめでとう。
The honorific "o (お)" or "go (ご)" can be attached to the front of some nouns as a formal way of saying "your". It is very polite.
To somebody who is sick
Guai wa ikaga desu ka.
具合はいかがですか。
Kaze wa dou desu ka.
風邪はどうですか。
Okagesama de yoku narimashita.
おかげさまでよくなりました。
"Okagesama de (おかげさまで)" can be used whenever you announce good news in answer to someone's concerned inquiry.
Odaiji ni.
お大事に。
To reply "Odaiji ni (お大事に)", "Arigatou gozaimasu (ありがとうございます)" is used.

