According to the Julian Calendar, it's Christmas on January 7.
After leading the midday Angelus on the feast of Epiphany, January 6, Pope Francis extended his best wishes to those who celebrate according to this calendar:
I extend my heartfelt best wishes to the communities of the Eastern Churches, both Catholic and Orthodox, who celebrate the Nativity of the Lord tomorrow.
In a special way, I would like it to reach the brothers and sisters of the suffering people of Ukraine. May the Lord’s birth instill comfort, instill hope; and may it inspire concrete steps that can finally lead toward the end of the fighting and to peace. Let us pray a lot for Ukraine and for peace.