In reply to Peter Lancashire.

Thanks for writing. Yes, different countries celebrate different holidays. Furthermore, new holidays can be created, as was done in 2021 in the US with the creation of the Juneteenth holiday. Furthermore, it can be a programming challenge to predict the future date of any non-fixed holidays such as Rosh Hashanah, Easter, and Eid, which are based on lunar calendars and can even vary from country to country.

However, if you can get the dates into a data set, the technique in this post can help you to plot them.