To add closed captions to your video:
Click Generate on your video.
Use the toggle Burned-in captions to enable closed captions to be displayed.
Select the blue Generate button.
Captions will be included on the video and these will not be able to be switched off by the user.
To learn how to edit your captions, see: How do I edit closed captions on my video?
List of languages for closed caption can be found here
Notes:
Use the video 3-dot menu to download your video subtitles/captions once the video is generated.