Instructions
Power on the Wii. You'll be brought to the Wii Channel Menu.
Use the Wii Remote to navigate to the "Wii" button in the lower-left of the screen. Press "A."
Select the "Wii Settings" option. It's indicated by a wrench icon.
Click on the blue arrow twice. This takes you to the third system settings page.
Choose "Language" and press the "A" button.
Hover over "English" and press the "A" button to select it.
Hover over "Confirm" and press "A" to finalize your choice. All Wii menus will now appear in your chosen language.