One solution (the one I'm using at this moment) is to manually download the subtitles with some utility prior to watching (Google2SRT comes to mind, or youtube-dl) and select them within the "Audio - Settings" submenu of the "Player controls" OSD menu ([M] key or move the mouse), after starting the video:
(click the speaker-shaped icon)
(this window appears, select "Browse for subtitle..." and pick up the file you've just downloaded with Google2SRT or youtube-dl)
The major caveat is it's only good if the video is from a channel you watch regularly or you've subscribed to, not for a video that you'll pick up randomly. Plus you must do this manipulation again each time you watch a new video (rewatch an old one). Not ideal, but better than nothing, and it works.