I added JC Helary’s French and Japanese transcript to https://emacsconf.org/2021/talks/omegat/ as a way to demonstrate how that might work for volunteers who want to translate any of the #EmacsConf talks. (Early access in the backstage area!) The video already had selectable text tracks. At some point, I should probably figure out how to code it so that clicking on a caption switches the video to the appropriate text track. =)