ARABIC ميلاد مجيد (miilaad majiid)
CATALAN bon Nadal
CHINESE 圣诞快乐 (shèng dàn kuài lè)
DANISH glædelig jul
DUTCH vrolijk Kerstfeest
ENGLISH merry Christmas
ESPERANTO gojan Kristnaskon
FRENCH joyeux Noël
GERMAN frohe Weihnachten / fröhliche Weihnachten
GREEK kala christougenna / kala xristougenna
HEBREW חג מולד שמח (hag molad saméa’h)
HINDI Krismas ki subhkamna
INDONESIAN selamat Natal
ITALIAN buon Natale / gioioso Natale
JAPANESE merii kurisumasu
KOREAN seun-tan chu-ka-hae-yo
LATIN felix dies Nativitatis
PERSIAN krissmas khojaste / krissmas farkhonde
PORTUGUESE feliz Natal
RUSSIAN С Рождеством Хрисовым (S Rojdesvom Khristovym)
SPANISH feliz Navidad
SWEDISH god jul
What a lovely list, thank you!
CZECH veselé vánoce
SLOVAK vesele vianoce
just to add for the Japanese one ; メリークリスマス
Lietuviškai - su ateinančiom šventom kalėdom 
NORWEGIAN - God Jul! (Happy Christmas!)
I am not a native speaker.
The most current form for Christmas wishes in Italian is “Buon Natale!”
Slovenian: Vesel Božič!