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