That's the feature I am most interested in. I've sold my Japanese Wii U a few months ago because having to deal with the files and region of every single game, without any guarantee that the game will actually work, was a pain.
Maybe with aroma it is time to start searching again for that 32GB...
Yeah don't do that, editing sys_prod can be dangerous and result in a brick.
Kirby, Mario Kart 8, Super Mario 3D World and some others can be set to spanish if you decrypt the game and change the Japanese language files to the Spanish/English ones from the EUR/USA version. And as i said...
I've dealt with the same problem in the past, even if I was able to run some games like Wind Waker HD, NES Remix or BOTW in spanish with Spiik, others like Twilight Princess HD, Mario maker or Splatoon only boot in English, and when i use Spiik either the game still boots in English or freezes...
although i ended up accidentally changing my nand with no way of going back bc i didn't know you needed a gamecube controller to restore it (i have a wii minus/1.1, which doesn't have gamecube controller support)
and if i find the sd card i have my NAND backed up on, i can not only restore the NAND if i solder the right part in, but i can also put my NAND on dolphin, then i can play dolphin online, like PMEX Remix or MKWii Riibalanced