For those of you with multi-lingual web sites, you want to make sure to keep your languages set on each URL of your web site. Try not to have some English and some French on the same page, keep the different languages on different pages when possible.

A Google Webmaster Help thread has Google’s JohnMu clearly saying you do not want two different languages on the same page. He said:

Of course, there are exceptions.

Forum discussion at Google Webmaster Help.