I could see it being a lot more useful for Japanese or other no Latin alphabet languages. Especially for the kanji. I’m too early in Japanese to watch content.
I don’t think I count as a polyglot (Native English, Spanish proficient, learning Japanese and German) but what is that even useful for? I feel like it’d be really confusing to have two subtitles for the same dialogue.
I just watch, in whatever language I want to practice.