On the subtitles page, you can choose whether your content has hardcoded subtitles burnt into the film as shown in the first image below. You can also upload your own subtitles by following this guide. Subtitles are optional, so you don't need to include them.
To add subtitles to a film you’ll need the subtitles in either SRT (SubRip Text) or WebVTT format.
Go to the ‘Media’ tab and select ‘Films’.
Select the film you want to add the subtitles too. Select the ‘Captions and Subtitles’ tab.
Select the ‘Add a Subtitle’ button. Enter the language of the subtitles, enter the display name, select the file, and click the ‘Upload button'.
The display name is how the subtitle language will be displayed to users.
Optionally, refresh the page to confirm the upload was successful. The status will be set to ‘Completed’ if the upload was successful.
The same process above can be used to add closed captions to a film.