Changing languages in LoR is a snap, so long as you haven't quite logged in yet. In the client, just take a peek at the top left, and you'll see your chosen region. From there, you can change the language displayed in-game.
Already logged in? No worries. Logging out is pretty easy, too. Head into settings (the gears in the upper right-hand corner). Go ahead and select Logout and confirm your selection by clicking OK.