If you click on the sprockety looking thing up in the upper right corner, it should take you to settings. Then click Basic Settings. Language is the first drop down box; you can reset it to English there. You may have to reload the page.
On the Inbox page click on the gear icon in the upper right corner of the page, then on Settings. On the next page click on "Basic settings", and check to see that English is set as the default language.