Ok, so the secret was to copy the Hotfix/Game folder into C:\Riot Games\League of Legends\Game ONLY after you start the LOL client, because "everytime you start the LOL client the game folder rewrites/reupdates/repatches itself, so everytime after you start the lol client you have to recopy the game folder.
For english users look this video, this helped me out:
Have fun ! And never use it on main !