Many Google services on the google.com domain will try to detect your location and customise the results using the local language. This caught me out a few days ago when I was using a guest Wi-Fi connection at Microsoft and got the Google homepage in Dutch (presumably Microsoft UK’s Internet access is routed via the Netherlands) and tonight I fired up Google Reader in my hotel room and found it was in German (I’m using an iBAHN Internet connection).
Not to worry – just manually change the top level domain in the browser address bar to use a specific country (e.g. I switched from http://www.google.com/reader/ to http://www.google.co.uk/reader/) and the interface should switch to the chosen locale.