devtrackers.gg
Hi @coralreece and welcome to the forum.
I'm sorry to hear that Russian is not available for you in Assassin's Creed Valhalla.
As mentioned by Ubi-Woofer there are multiple regional versions of the game. With a disc version you generally purchase the regional version that is available to you in your local retail stores, however in some cases it may also be possible to purchase other regional versions of the game online. Where as with a digital version you would automatically receive the version for your region, therefore you would be unable to change this and Russian would not be available to you if it is not shown in the game.
The supported languages that are shown on the Microsoft Store are likely to show all of the languages that are supported, apologies if it does not specify specifically which languages are supported for the version you purchased.