There is a big difference between loading a japanese game on a north american wii, and loading an american game on a european wii.
This difference is called TV signal. Japan and NA both use the NTSC video standard... meaning that they both put out visual data in the exact same way... Where as Europe uses the PAL standard.
That said, many (but not all) Wii games have both video modes coded into them... so simply changing video mode in your backup loader will work fine. Other games don't have both NTSC and PAL signals programmed into them, thus if you try to play a PAL game on an NTSC TV it will likely black screen.
Many modern TVs (NA and PAL) support both video modes (though sometimes not fully.... my HDTV plays PAL signals but with the button portion of the screen cut off... but at least the colors are right
).
Basically, if you're in luck either your TV supports NTSC and PAL signals which is the best option because then the game doesn't have to be patched to play... or the game itself has both video modes in it (which can still be buggy on a few games since PAL games are never designed to run out of region)