The language of the audio track, the subtitles, or closed captions file. The language code must be compliant with [BCP 47](https://datatracker.ietf.org/doc/html/rfc5646). This property is mandatory if the input provided is of type SUBTITLES or CLOSED_CAPTIONS and recommended for input type AUDIO and an input that does not specify an input type (combined audio and video). If an audio input does not specify the language, it is defaulted to `und` (undefined).