Až opět zprovozníš hru, tak zde je poslední možná šance, dál už nevím

Step 1: Start the Multiplayer of Assassin's Creed IV.
Step 2: Switch to your desktop again. (Alt + TAB)
Step 3: Copy an original multilanguage "localization.lang"-file and paste it into your Russian Assassin's Creed IV folder. (I can provide the localization.lang if you want)
Step 4: Switch to the Multiplayer again, and press "Switch to Singleplayer".
Step 5: Enjoy your language. You can now choose your language in the options.