It's an open congress put on by a German club, and people giving talks aren't being _told_ to give talks in German. If someone is more comfortable presenting in their native language, why shouldn't they?
communication is a 2 way process. Languages are just a tool. One might be proficient in one language but it may still not be the best tool for reaching a wider audience
How dare the Germans organize an event in Germany insist on speaking German.
Their target audience is global. Plus, those talks are virtually like a curriculum vitae or portfolio for those speakers. They are only limiting themselves. I speak 5 languages & I would never use anything but English on internet, but that's just me, I prefer to be understood by 99% instead of 1% of my audience when I speak.
No, their target aufience is German. CCC is German. Their target audience for these talks is the live audience which consists of a variety of different ethnicities, but it is dominated by the german hacker clubs which form the CCC. Have you ever been to a chaos event?