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:
In general, we recommend sticking to a single language per page. If you have multi-lingual content on your website, I'd recommend using separate pages per language. Our language recognition tries to find the most relevant language from your content, so that we can send you users searching in that language. Having the language in the URL (as Robbo suggested) is a great way to make the language of the pages clear to users, so if you can do that, it might make sense (Google determines the language based on the content, so it's not necessary for us).
Of course, there are exceptions.
Forum discussion at Google Webmaster Help.
