During the question and answer portion of a John Mueller hangout, a webmaster asked John about having two languages on the page.
The webmaster was ranking well for both languages (Hindi and English) until the December core update. Then the site dropped, mostly for Hindi keywords.
The webmaster was curious about what would cause this ranking drop and if there was anything they could do to correct it.
John said Google doesn’t recommend using more than one language per page. Instead, they recommend an implementation where you would have Hindi clearly on one page and English clearly on another.
If more than one language is used on a page, Google could misunderstand whether or not someone is searching for English vs. Hindi and not actually show the page as a result.
This conversation happens at approximately the 33:32 mark in the video.