The German department of Ubi Soft states that the European version of Rayman DS will feature an exclusive multiplayermode. Apart from the information that we're dealing with a 2-playermode, no information was released yet.

In the past, a press release from Ubi Soft already stated that "the European version of Rayman DS will include a multiplayer feature and will take full advantage of the touch-screen technology", however a real exclusive mode was not confirmed.

Update: France adds to the story.
Closer inspection of Ubi Soft France's website showed a little new fact on the European exclusive multiplayer option. According to the French corporate website, Rayman DS needs only one cartridge for up to 4 players multiplayer-fun.