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Here is an example for German Holidays. I use it with Calendar 5.5. You can copy the code of the attachment to your Holiday.php.
Some Holidays depends on the easter sunday. This Holidays are calculated by the function easter_date. Therefore there is no need for a special Holiday.php for each calendar year. Code example (not the complete Holiday.php):
The php function easter_date causes a warning for time before 1970 and (on systems with 32 bit) after 2037. Because you can see only the actual year and the year before and after I think there is no need for a special handling of the function limit. And in most cases we have 64 bit servers.