[i18n-activity] Metadata examples do not include xml:lang (editorial)

aphillips has just created a new issue for 
https://github.com/w3c/i18n-activity:

== Metadata examples do not include xml:lang (editorial) ==
https://w3c.github.io/ttml2/spec/ttml2.html#metadata-vocabulary-metadata

There are several examples of `ttm:title` or `ttm:desc` containing 
natural language text, but no `lang` attributes are supplied.

Please view or discuss this issue at 
https://github.com/w3c/i18n-activity/issues/325 using your GitHub 
account