In Austria, we tend to split it between "Merry Christmas" for the 3 Christmas days and then on Dec. 31 we say "Gutes/Schönes/Frohes* neues Jahr" (Good/Happy new year) or "Guten Rutsch" (Have a good slide or ride).
"slide/ride" as in "slide/ride into the new year".
* "frohes" is a term that mostly (northern) Germans + people from Vienna would use though.
In local dialect, I would just say "Guads nojs", which means "Good new (one)".
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I would never say "Happy holidays" (Schöne Feiertage ?) though. Sounds weird, or something like a person from (northern) Germany would say.
Voted for "merry Christmas".
I don't think this poll is really relevant for other languages than English.
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