This document purpose: display dual language subtitles on YouTube, in Chinese and English.
Install the Dualsub extension, then open a YouTube video, use this video as an example.
Make sure the video subtitles can be turned on normally.
This video has 36 subtitles, the English subtitle is turned on.
Click the Dualsub toolbar button, switch to the Free Mode tab.
On the left, 1 and 2 are subtitle line numbers, indicating that two subtitles can be turned on.