I found how to download the subtitles from a YouTube video. Whether the subtitles work I don't know.
Go to the video and open the developer tools using F12 on the keyboard and click network. Make sure the Network is empty if not there is a trash can button to clear the network. Then click the CC button on the video. You should see a new entry appear :
Open this link in a new tab and a dialog will come up. Name it the same as the video and give it either a .srt or .vtt extension.
I haven't tested if it works so perhaps someone can try it out.