I've bought a Russian (16$) key and had a friend activate it for me. Works perfectly well and you can download an English version from steam if you select your steam language as English and the game's language as English. Used Russian keys in mw2 and black ops as well. Only had minor issues with dlc's in black ops.
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!