Hello,
I finally got my keyboard fixed. After few weeks to try many different things which didn’t work, I gave up, and went to a fixing shop.
I have been to 3 shops and they said all the same: the problem was the motherboard, when I unmounted everything I damaged it. I’m sure it’s because I didn’t pay attention enough of the videos I watched: the keyboard cable was hidden under the speaker cable. So pay attention guys, at that place there are 2 cables to remove! Not one!
Thankfully I live in Shenzhen and here the reparation cost for electronic are affordable: equivalent of 40 euros to fix the motherboard, replace some screws and rubber washers which were oxidised/broken, and make the percentage of my battery working (for the battery seems just a SMC reset with the newly working keyboard made the trick, with the usb keyboard plugged I couldn’t reset the SMC).
This MacBook version is pretty a mess to fix and to unmount. If you are very careful, have proper tools (mine were so so, so next time I will order iFixit kit), watched several times videos, you can do it, otherwise ask someone to do it for you.
Replace by yourself the battery is actually much easier than unmounting the motherboard, just pay attention to the touchpad, after it will be just annoying to remove the battery tape. But again, still pay attention to the touchpad, my friend got replaced his battery at a shop few weeks ago, and once he went back home he noticed that the touchpad was not working well on one side… The battery replacement is totally feasible, just follow the recommandations of iFixit and use their tools.