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?