> Popular search engines such as Google, Bing, Yahoo!, Wikipedia, Amazon, YouTube and Baidu are used to calculate the ratings.

This bit is partially inaccurate. They don't actually use Baidu, Yahoo, or YouTube because they can't parse a count of search results from those sites' search pages.

They do, however, include the number of hits for "<language> programming" on the Amazon search page... as well as on eBay, microsoft.com (i.e. Microsoft's support pages), Walmart, and Etsy.