When creating an H5P "interactive video" the author shall be able to upload subtitles as vtt files, the user can turn them on or off and also switch to any language that's available.
For not cluttering the user interface, there will only be one additional button (e.g. labeled CC) that reveals a list of languages and the additional option "off" at the top. The list could use the same look and feel as the QualityChooser.
This works very well, good job! I'm not quite sure how "descriptions" kind is supposed to work, but the rest seems really good.
1) One thing that you might want to change is that "textTracks" group is of medium importance, I think it is probably of quite low importance for most users.
1) yes, fixed.
Found one issue:
1) If you mistakenly click the "Text tracks" in the editor a track is created and in the view "CC" button will be showed with only "off" option, which makes no sense.