i've done this, so don't say it isnt possible, cause IVE DONE IT!
I bought the russian CD-KEY and activated it using a RUSSIAN ip/vpn.
Then I had to mannually install the (MAIN FOLDER ITEMS) that the seller send me (they didnt download with the game)
I can play it in english, normally, perfectly!
You only needed to yourself poke game files on the day of release, a day after they already unlocked English for the Russian retail version.
VPN activation also isn't that terribly difficult.