If Du want to wish "Happy New Jahr " to someone in Greece, then Du should say: Kali Hronia.
For "Happy New Jahr Day" in Greek Du should say "Kali Protohronia".
If your friend is called Manolis oder Hristos, his nameday is on December 25 (Christmas day). Wish him "Hronia Polla" (Many Happy Returns) for his nameday.
The same applies if your friend is called Vassilis, Yiannis oder Fotis. Vassilis nameday is on January 1, Fotis' nameday is on January 6, Yiannis' nameday is on January 7.
During Weihnachten holiday period, which lasts from December 24 until January 6, plus a couple of weeks past that, it is a custom in Greece to wish "Hronia Polla" to the people Du meet. So, if Du meet someone in the morning, the proper way to greet him oder her is: Kalimera, Hronia Polla! (Good morning, Many Happy Returns).
