srclang

srclang is an HTML attribute used on the track element to declare the language of a text track, such as subtitles or captions. The value is a BCP 47 language tag (for example en, fr, en-US).

The track element associates metadata with media elements; srclang informs user agents, accessibility tools, and search engines about the language of the track's text. It is common to pair srclang with label and kind attributes. The value should be a valid language tag; codes may include region or script subtags, such as en-GB, zh-Hant, or fr-CA. If omitted, some user agents may have difficulty presenting language choices reliably.

Example:

<video controls>

<track kind="subtitles" src="subs_en.vtt" srclang="en" label="English">

</video>

In standards, srclang is defined in the HTML5 specification (HTML Living Standard). It is supported by major modern browsers and is considered best practice for multilingual media to aid accessibility, assistive technologies, and automated indexing. While not always strictly required, providing a correct srclang enhances the user experience by enabling accurate language selection and improving the discoverability of multilingual tracks.