It isn't. There is a German, a French and a English version of the talk online and the original Audio seems to be in English (note the gear icon on the lower right corner of the video).

The original talk was held in English, but there are translations in French and German available as well. Please have a look at the settings icon of the video, you can change the language of the talk there.

It's originally in English with German and French translations also available. You can use the cog icon to select a different stream if it defaults to the wrong one for you.