The books the Netflix series 'The Witcher' is based on are written by Polish author Andrzej Sapkowski. Netflix creator of the series has created several dubbed and subtitled in other languages. 

Esperanto is a language created by L. L. Zamenhof who lived in modern day Poland. The goal of the language was to allow people from different backgrounds to communicate with each other to decrease violence.

Today, people can learn Esperanto online including Duolingo. There are about 300,000 people learning Esperanto on Duolingo. However, few films and tv series exist in the language. 

By Netflix offering a subbed and dubbed version of The Witcher in Esperanto, people learning Esperanto and fluent speakers can enjoy the series. This would also increase watch time on a series Netflix has already developed.