A user of Youtube compared the popularity of the Japanese celebrities by the number of articles on Wikipedia. Surpassing the prime ministers and the emperors, an anime singer Mizuki Ichirou ranked the top in the ranking. His article was written in 91 different languages.

The popularity ranking of Japanese on Wikipedia (Youtube)

Top 10 of the ranking
Rank/ # of languages/ Link to Wikipedia
*1, 91 Mizuki Ichiro
*2, 71 Kurosawa Akira (film director)
*3, 64 Hirohito (Emperor Shōwa)
*4, 62 Matsuo Bashō (poet in the 17th century)
*5, 54 Akihito (the current Emperor)
*6, 53 Koizumi Junichiro (former prime minister)
*7, 51 Fukuda Yasuo (former prime minister)
*7, 51 Katsushika Hokusai (artist in the 18th century)
*9, 50 Abe Shinzō (former prime minister)
10, 45 Murasaki Shikibu (novelist in the 11th century)

The frequency ranking of the revisions of Wikipedia articles reflects the nationality well.

Japan (2007)
1, List of One Piece characters
2, Mai-Otome
3, One Piece
4, Bleach
5, Gintama
(35, Japan)

US (2006)
1, George W. Bush
2, Wikipedia
3, United States
4, Christ
5, 2006 Lebanon War

France (2006)
1, April 2005
2, December 2004
3, Algeria
4, France
5, Wikipedia Top page

Source: Scan of Nikkei