According to Marketo, the new release isn't going live until the evening (Pacific time) on 1/11/13. You'll need to wait one more day! Then, from the My Marketo screen, click the What's New tab, and it will tell you where to change the langauge (hint: You can find it in Admin...)
EDITED: We do a staggered rollout and some pods in Europe have already been upgraded. If you received a notification that you were being upgraded on Wednesday then you have the new features. To change the user language which will override the subscription language, but only for you, do it under my account which can be accessed in the top right of the screen by clicking on your name.