The game is the first third party Wii party to reach the milestone.
http://www.nintendoworldreport.com/news/27442
Ubisoft's Just Dance 2 has becomes the first non-Nintendo-published title to sell more than five million copies on the Wii, according to sales data by the NPD.
The dance title, which was originally released in North America on October 12, 2010, finished third for the month of July, selling 120,000 units. This makes Just Dance 2 the eighth Wii game to reach the milestone, and the first third party game to do so on the system.
Previous five million selling titles include Wii Play, New Super Mario Bros. Wii, Super Smash Bros. Brawl and Wii Sports Resort. A third Just Dance game is scheduled to be released this fall.