how to have holidays of different countries shown on OS X default app? I have US holidays and in the settings there is Chinese calendar too. But I want to have holidays of a few different countries included in the calendar simultaneously. Is there a way to do this?
Apple has a website with all supported calendars.  You can download and install dozens of different types of calendars on your Mac.  

Simply find the calendar you want to use, download it, and then install it into your calendar. If you sync your calendar with iCloud, these dates will also be added there.  If you don't know how to do that, see this Apple Support site for directions on how to add calendars.

If you have any iOS calendars that sync to this calendar, they will also be updated with the new dates.