Subtitles display timed text alongside video, often to translate dialogue or make speech readable. They can be carried in different formats, supplied as separate tracks or burned into the picture. A player's subtitle button can select only supported text actually available in the presentation; it cannot generate every requested language from an absent track.
A practical example
A film can include one subtitle language while another edition includes several. A viewer using the same app may therefore see different choices from title to title without the subtitle control itself being broken on the device.
A common misunderstanding
Do not confuse a menu's interface language with subtitle availability. Changing the app's display language does not automatically add a translated subtitle track to the programme being watched.
Related terms
Stable technical definition. Editorial approach