Yes, it's possible, and done on some wikis like fr.wikipedia, but please get a consensus on the different Russian projects to support this request (leave a small message on the village pump of each ru.* for example).
The setting is per language, not per project, so it will be also served when another site like de.wikipedia or Commons is browsed in Russian.
So, if I've well understand the ru. last comments, there is a preference to upload a stabilized Russian translation to the WMF site?
The policy provides the following statement:
And as an header of the translation:
Это перевод. Официально утверждённую версию этого документа можно увидеть по ссылке на англоязычный оригинал.
So, the official and binding version is the English one, any translation, wherever published, on meta or Foundation, won't be official.
So I'd suggest to deploy it and to ask ru.wikipedia community to locally override the MediaWiki message, to watch how the page evolve in the future and when they feel it's not a vandalism target to remove the overwrite.
No opposition for one month recorded, and a consensus on the different Russian projects, so we can live the change. I've removed the CR -1. If quickly merged, it will reached ru. projects this week (Wednesday most, Thursday Wikipedia).