Select the (gear icon) dropdown for your installed Editor version and click Add Modules . Find the Language packs section and check Russian .

Are you trying to download the for game development, or

If you are looking to fix or add Russian language to the game Assassin's Creed Unity (often for region-locked or Steam versions), the process usually involves modifying game files.

While the official Unity Editor is primarily in English, there is an "Experimental" feature to enable other languages, including Russian, via language packs. Open Unity Hub and go to the Installs tab.