In the beloved N900 you could install the holidays to the calendar as follows:

going on the website

http://www.mozilla.org/projects/calendar/holidays.html

choose the country that interests you,

selecting "open with calendar,"

choose the calendar to which you want to add holidays (N900 is generally synchronized - otherwise choose private or one that you've already created or will create a new one) and just made, the holidays have been added.

Personally I'd created a new calendar called "holidays", because then I could enable or disable it at will, and highlight the holidays in a different color in the widget and the calendar.

Now I wonder if you can also do this in ns. N9.