Answer
The control’s tooltip says Hide Captions or Show Captions. There is no subtitle-language menu or caption-details gesture. Captions follow pause, seeking, playback speed and looping, and sit above visible playback controls. Hiding captions lasts for that viewer session; reopening turns them on again. Picture-in-picture captions are not guaranteed.
Each video copy has one current subtitle track. A successful request in another language replaces that copy’s previous subtitles; a failed request preserves them. An older slower request cannot replace a newer successful one. To change language, request new subtitles with Text AI.
Current web, phone browsers, iOS and Android support these captions; older installed builds may retain their own controls and downloadable files.