I was going to link the book because I thought it was on the Public Domain, but apparently not in every country [1]. Also, the site you reference seems to be purposely misguiding visitors by omission about the book's licensing status [2].

[1] http://www.communia-association.org/2015/01/23/the-little-pr...

[2] http://www.thelittleprince.com/licensing/