I am aware that a similar request already exists about holidays. I think that more calendars should be created and made available to suit specific user subgroups. For example; individual religious calendars to add in Bhuddist, Christian, Islamic, Jewish, and Shinto observances. Another one for bank holidays, another one for groups like UK holidays, EU holidays (US Holidays already exists), and then subgroups for individual national holidays. This would give users a wide range of flexibility without daunting complexity or the clutter and constraint of a few add-ins of large groups of holidays.