Language tag to associate with the track corresponding to the receiver
- iOS 7.0+
- macOS 10.9+
- Mac Catalyst 13.0+
- tvOS 9.0+
The value is specified as an RFC 4646 language tag; can be
nil in which case no tag is written to the track.
Extended language tags are normally set only when an ISO 639-2/T language code by itself is ambiguous, as in cases in which media data should be distinguished not only by language but also by the regional dialect in use or the writing system employed.