Google Maps, like most web apps, incorrectly determines my language based on IP address. I can't find a way to change it from the UI, but you can force it to English with this:
If you use Chrome, and are not logged in to a Google account, Google Maps respects the Chrome language setting (just tested). Go to settings, "Show advanced settings" at the bottom and search for "Languages".
If you are logged in to a Google account, the language settings on your Google account takes preference.
That isn't the case for me. I have my OS and Chrome set to English [0], but when, in Incognito mode, I go to http://maps.google.com/ it redirects me to https://www.google.it/maps/ and displays everything in Italian (I'm in Italy at the moment).
If you are logged in to a Google account, the language settings on your Google account takes preference.