Exactly same problem here.
Recently decided to remod my wii, which was modded years ago by some local vendor. Everything works fine till yamnME can't detect the system region. Konami code couldn't solve it either.
Thanks a lot to
@peipei_02: it was very helpful to know that YAWMM would work.
However, even after all the IOSs were successfully updated or stubbed, the problem still exists. The app RegionChecker can't determine the machine's region as well.
One suspicion for the root cause could be some unknown remnants from the old mods that I didn't manage to fully erase.
But I only found a few cases addressing the same problem like this thread: [yawm-couldnt-find-the-region-of-this-system.64611]
and they all happened to have shop code 128 (Taiwan) in common, makes me wonder if that could be the cause.
(The official Taiwan edition Wii is basically the variant of Japan edition that goes with J system menu, seems to be often neglected by homebrew apps. Not necessarily a problem unless region check is strict, I guess.)