Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
April 12 Easter
April 13 Easter Monday
May 01 LabourDay
May 21 Feast of the Ascension
May 31 Pentecost
June 01 Pentecost Monday
July 21 Belgium_NationalHoliday
August 15 Assumption
November 01 All Saints
November 11 Armistice
December 25 Christmas