In Hebrew, the name of a holiday isn't usually included in its greeting. So Hebrew speaking Christians would just say "Happy holiday" or khag same'akh (חג שמח).
Just as in your question !They tend to say "Happy Christmas" instead of "Merry".Merry Christmas
You say ' Merry Christmas' in the UK.
merry christmas
merry christmas
Merry christmas
Merry Christmas
"Merry Christmas"
merry Christmas= Christmas aashamsakal
Hanukkah is a holiday, not a language. You cannot say "Merry Christmas in Hanukkah. That's like asking: "How do you say Merry Christmas in Easter" I think he means how do you say merry Christmas in Hebrew
Merry Christmas
Merry Christmas
Merry Christmas