You do notice that all of the countries listed as "Very High Proficiency" are Scandinavian or Dutch, just like he said, right? And many of the continental European countries, like France, Italy, and Spain are listed at only "Moderate Proficiency."

While you don't need perfect language skills to understand technical concepts, not being at full proficiency can be a barrier. I know that when I help people out on StackOverflow, one of the main barriers to answering some people's questions is that they can't formulate it in English in a way that I can understand. Proficiency is a two-way thing; besides being able to read English, you need to be able to speak and write it well to fully interact with the technical community.