The cdkey must be entered in registry, but its in binary. To get the game to run, I installed under wine/lutris, exported the key named "key" under "[HKEY_LOCAL_MACHINE\Software\Wow6432Node\bohemia interactive studio\arma 2]", then started the registry editor under the game's prefix ((WINEPREFIX=~/.steam/steam/steamapps/compatdata/33910/pfx/ regedit)). Import the reg file containing the key only, and launch the game with the registry editor still open. A few secs after clicking "play", close the registry editor and the game will start. Unfortunately this has to be done before every launch of the game, because the key is apparently cleared every time the game starts.