With Dual Caption you can easily display 2 subtitles on all YouTube videos with multiple subtitles. You can also use this extension with video’s that have no or subtitles. To do this, open the YouTube caption and translate the subtitle (or automatically generated caption) into the desired language (using YouTube caption translation). The translated subtitles will not appear in this extension. So select the translated caption on YouTube and choose the original caption in the extension. This way you can get two subtitles on video;s without subtitles.
This extension has a shortcut key ( Alt + D ) for easy switching on/off of the second subtitle. You can enable it via the extension options. It also gives you options to adjust the appearance of the captions. From the extension options, you can add space between the captions use a custom color for each caption and change the text size for both captions. Click Here to install this extension.