The resolution of bug https://www.w3.org/Bugs/Public/show_bug.cgi?id=15922 added the <lang> tag to WebVTT. http://dev.w3.org/html5/webvtt/#webvtt-cue-language-span http://html5.org/tools/web-apps-tracker?from=7503&to=7504
<rdar://problem/12644159>
This was fixed by bug 108858. *** This bug has been marked as a duplicate of bug 108858 ***