Wikipedia is a crowd-sourcing phenomenon. It has over 77,000 contributors working on more than 22 million articles in 285 different languages. The way the site works, disputes are settled via collective voting and editorial collaboration over information and wording, sometimes in back-and-forth word wars that are often dubbed “Edit Wars” on the site.
Tracking these edits, we can see what topics are the most controversial overall, no matter the language. Most of these Edit Wars take place in the English version, which is by far the largest Wikipedia edition, with over 4 million articles online. It should be noted that controversy is often regional, however, with some of the most contested articles being language-specific.
According to Taha Yasseri and researchers at the University of Oxford in the United Kingdom, who compiled lists of the most controversial topics (measured by Edit War numbers) in each language, the most controversial subject today is George W. Bush. Followed, interestingly, by Anarchism and then Muhammad.
Worldwide, no matter the language, the most controversial Wikipedia articles tend to be religion-based, with the big three Judeo-based religions (especially Christianity and Islam) ranking in the top five consistently. Topics like Global Warming and regional entertainment figures or companies are also often ranked in the top five.
The Oxford groups are continuing to study these Edit Wars and how they reflect the cultures that surround them. You can read more about this in their paper The Most Controversial Topics in Wikipedia.