Hello Gotishe,

saw the answer here:
https://forum.faforever.com/topic/5226/

To change language in the FAF client:
click hamburger button at top-left
click "Settings"
click "Language"
select Russian

To change language in the game itself:
while the game is running, click the circle button at the top of the screen
click "Options"
click "Interface"
click "Language"
select "RU"
(after selectiong the new language you need to restart the game)