How can I correct/delete iOS holidays on iDevice
AFAIK, you cannot delete the Holiday Calender on your iOS device. However, you can hide it via Calender app. In the Calendar app, tap Calendars in the bottom center and uncheck the Holiday calendar. And, here's how you can add Austrian holidays to your iPhone and iPad calender:


Go to Settings -> Mail, Contacts, Calendars
Now, tap on Add Account
Scroll down and tap on Other
Tap on “Add Subscribed Calendar”
Type in “http://laudatio.com/florian/ical/AustrianHolidays.ics” and press “Next”, and then press “Save”
Press "Done". Congrats, you've added Austrian Holidays to your calendar.


You might find this useful: http://www.igeeksblog.com/how-to-add-us-holidays-to-iphone-calendar/ Hope it helps!

FYI: My iPhone has a calender for Indian holidays.