If talking about being on leave from work or school, I would say I'm on holiday. I might also ask someone what they did for their holiday, or where they went on their holiday. Using the plural "holidays" is a bit antiquated. For national public holidays, I would usually mention which holiday, such as "Are you seeing your family for Christmas?", "Are you going away at Easter?", or even "Are you going to watch the Australia Day drone show?"

One thing to note is that “holiday” is used differently in American English. In American English, “holidays” refer to celebrations like Christmas, Thanksgiving, Independence Day, etc. Ex: “My favorite holiday is Halloween” or “Monday is a holiday (Labor Day) so the office is closed.” To speak about traveling, an American would say “I’m going on vacation” or “I took a vacation”