Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 11 Easter
April 12 Easter Monday
May 01 LabourDay
May 20 Feast of the Ascension
May 30 Pentecost
May 31 Pentecost Monday
July 21 Belgium_NationalHoliday
August 15 Assumption
November 01 All Saints
November 11 Armistice
December 25 Christmas
DateTimeExtensions DateTimeExtensions