We use Vimeo to play the video in the page. If you click on the video itself, the controls for the video will appear. To the right of the controls is the 'Subtitle' button.
On mobile, there are two different methods depending on if the video is playing or not.
Mobile method 1
When the video is not playing in fullscreen mode, you will see the closed_caption icon, for 'Closed Captions'.
Click on that to launch a menu.
And select the desired language.
Mobile method 2
When the video is playing, or paused, it launches in fullscreen mode. This mode has different buttons, but the concept is the same.
Tap on the screen to bring up the controls, on the far right is a speech bubble icon:
Click on that and a menu will launch:
Select your desired language, and continue watching.
On the desktop, the icon is closed_caption for 'Closed Captions'.
Click on that, and a menu will appear:
Select the desired language, and press play.