You can't add old Nintendo friend codes for use on Wiimmfi any more, because too many people tried to abuse it with fake friend codes. You have to either use a new profile, or clear your friend code from your savegame. There should be a tool somewhere which does that, but I don't remember where.
Seit Mai 2016 finden auf Wiimmfi regelmäßig Mario-Kart-Wii-Wettbewerbe statt! Klick hier für weitere Informationen.
Since May 2016, there are Mario Kart competitions / tournaments on Wiimmfi! Click here for more information.