http://www.demo-it.net/wii-unity/
Is Nintendo's official SDK is absolutely necessary to develop a Wii game? I see the Unity and par …?
… They have everything I need to make games for Wii.
Yes In order to develop a game for the Wii, you must become a licensed developer for Nintendo and get a developer kit. This process usually takes time (3-4 weeks) and dev kit costs at least $ 2k. From there you can develop your game from the SDK for Nintendo Wii using tools or software licensing can create the game engine to make this go much faster (eg, even or Unit). To give this SDK, you must be a developer Nintendo authorized, so you can not skip this step.
Mario Kart Wii – Unity GPs part 1