All talks will have real time sub titles and some even have live voice translations. And you do Not have to speak German to attend, there will be enough interesting people with whom you can converse.

As someone who scored 22% on a multiple choice German test that he had actually studied for (if briefly), I can tell you that German is absolutely not required. There will be a few talks in German and the live translations aren't great, but there is more content in English than you can consume in four days.

(The joke is on me after I found a German girlfriend (not at congress), my German is now almost good enough to appreciate a talk in German.)

Most of the talks are in english and most people there speak english as well - I didn't have issues although my german is rather poor.