Oui. Google always act funny when dealing with language. Since it is a multilingual website, it constantly tries to detect your native language, so say if the next person using your computer types in mandarin, google will change its default language to accommodate that. If your Google is in French in the first place, you might have searched something in French and now google think you are gonna use French for a while. Usually searching for a few times in English will shift it back for you.
This has something to do with the search language preference, you can actually just set it in English and hope it sticks. Another source of the issue could be your location. Google search domain is automatically set to where you currently are, based on your IP address. If you are in Singapore, it will be Google.com/sg and for France it will be Google.com/fr. If you are in countries that speak two languages in the majority, like Canada where the second language is French, Google is more likely to set the language accordingly. So when your Google is in French, it is just Google messing up with its terrible language detection system.