The srclang property of the HTMLTrackElement interface reflects the value of the <track> element's srclang attribute or the empty string if not defined.
The srclang attribute is a BCP 47 language tag indicating the language of the text track's data.
A string.
const trackElement = document.getElementById("exampleTrack");
console.log(`Track's language: ${trackElement.srclang}`);
trackElement.srclang = "en-US";