Ora ho ArmA2 e i file delle mod ma, sinceramente, non ricordo dove vadano messi e come configurare il tutto per giocare in multi senza problemi 
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Installazione su Arma II/OA (non Steam)
Invece per Arma III:
Extract into the ArmA 3 Directory, by default this is located in:
32-Bit - C:/Program Files/Steam/Steamapps/Common/ArmA 3/
64-Bit - C:/Program Files (x86)/Steam/Steamapps/Common/ArmA 3/
After extraction it should look like this:
Steam/Steamapps/Common/ArmA 3/@your_mod_folder_name
When present place the "userconfig" folder into your game install folder, usually:
"C:\Program Files (x86)\Steam\steamapps\common\Arma 3".
You may already have "userconfig" folder from other addons/mods in which case it is safe to merge the contents from this archive.
You'll also need to add a Launch Parameter to Steam, in order to do so right-click on ArmA 3 and click Properties and then Set Launch Options. In the window that opens enter in -mod=@your_mod_folder_name
For using multiple mods you would then do so like this:
-mod=@mod_name;@mod_name2;@mod_name3;@mod_name4;@mod_name5
Note:
You can also use -nosplash to get rid of the splash art and intro videos.
Se invece vuoi fare le cose per bene installati un launcher. Ecco i link:
Arma II LauncherEd ecco quello che uso io per Arma III:
Arma III LauncherEnjoy!!
