When Translate finishes translating a page from language A to language B, the text in the DOM is replaced with language B.

However, the language attributes in the DOM still remain language A, and this breaks some accessibility features - for example screen readers try to pronounce the text of the page using language A.

Translate should update the DOM so that the root HTML element now specifies language B, and any other attributes specifying language A in descendant elements should be removed.

(It might make sense to leave alone unrelated languages C in other parts of the page.)