JP GC Retail disc on PAL Wii save problem

Hello. Im not so sure if Im in the right forum but I'll try anyway..

Long story. Sorry for that.

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Ive got some serious problems with an imported gamecube game (Donkey Konga 3) which i bought yesterday.
I started the game via neogamma (because of regionfree).

It worked for some seconds, until I came to the save screen.
Some donkey konga message in japanese (ofc) occured and i had no clue what to do.

In normal this is the point where you save you game, but in this case it was different.
After some resets and trying to press the "right answer", I found out that I deleted my entire memory card in Slot A and Slot B.
What a great start..

So the game tried to format the memory card to be japanese game compatible.
Funny though, because this didnt work out for me.
It still wont save.

According to a single related site I found in google, some guy fixed the problem by changing language and game starting language of the system to japanese by using AnyRegionChanger.
I tried that too. Different error messages than before, but still wont work.

I was so angry at that point I then changed my Area system language to japanese too, ignoring all the semi brick warning that WILL happen if I do that. But nothing happened. I haven't semi-bricked anything, or at least I haven't found anything that won't work. (The settings in the wiimenu doesnt work, shows an "opera doesn't found nintendo.co.jp"- error or so, but I don't care about that.)

I started the game again via NeoGamma. No changes at all.

I read somewhere something about NMM (No more memory) and DiosMios, so I installed that too.
But I have no real clue how to activate NMM. Starting NeoGamma again, game starts and
before I get the "Nintendo Gamecube Japanese Help Screen", I get another message from donkey konga I can answer with yes or no. I try yes and..
it saves for the very first time. I'm impressed. I reset by using the reset button to see if it worked.
And it did.

But.... now comes a very big BUT.

It will save and it will work too when I reset. When I restart my console by turning it to standby or by plugging off the power cord, the memory card will be corrupt and I have to reformat it again, in order to save the game. (Which makes no sense at all, because my save will be deleted everytime I do so..)

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Do you have any solution for me what to do..? I'm going insane..
Will it fix the problem if I get NMM to work? After all I'm thinking if it would be a better choice to pirate the game if this is the only way to use NMM. But this is extremely desperating.

Why the hell did I even import an original 7 year old game, deleted all my gamecube saves, when I cant even get it to work...? I don't know. Please help me. Is there any homebrew app out there to fix this problem somehow?
I don't have the skills to find something for me that works.

My system is (if this helps you) is a fully cracked Wii (I don't know which cIOS or what versions i have but every app I try works 100% in normal), with bootmii and everything. I already did a NAND backup before i did any of the above, just in case.