Read a horror book written by an author from each country in the world. To make it easier, you can use adjacent genres such as crime, thriller or general fiction with a dark subject matter (it's up to you how strict you want to be). Ideally, the book will have been published in its respective country and in that country's official language, but you can also use a book if the author identifies as being from that country. 
The list of countries was taken from https://www.britannica.com/topic/list-of-countries-1993160