Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 Ano Novo
April 18 Sexta-feira Santa
April 20 Pascoa
April 25 Dia da Liberdade
May 01 Dia do Trabalhador
June 10 Dia de Portugal
August 15 Nossa Srª Assunção
December 08 Imaculada Conceição
December 25 Natal