The widely used mechanism of using an IP address to guess the language of an user is not an exact science. It can also happen that if a lot of ZenMates from e.g. France use our German location large sites like Google "think" the preferred language for specific IPs is french or that the server the user is connecting from must be located in France.
This automatic recognition can be overwritten with a simple setting that is being stored locally in the browser.
Click here to change your preferred language when using Google.
You can also click here to use Google.com (International) directly.