Comment by ouchjars

Related tip if you won't/can't use this extension: Netflix shows normally have many more subtitles available than you get shown (and sometimes audio tracks). The selection you see depends on your interface language and locale.

For example, I can't use Spanish subtitles for one show (https://i.imgur.com/BBWuuPs.png) until I change my interface language to Spanish (https://i.imgur.com/bsyYJGR.png).