As i already stated in the italian forum.
This situation was caused by 2 enormous errors on your part, blizzard:
1) Allowing users to play in their language of choice with a russian key up until today, causing sellers to think they could sell RU keys as EU. Also allowing them now to say "blizzard did it, when we sold it it was a genuinely EU key" and keeping our money. The fact that they worked perfectly also caused other users to reccomend those sellers as legitimate ones, leading other customers to buy their keys.
2) Having one of your employees state that you can change the language in the russian version, when it was blatantly false.
With this patch you're effectively removing a core functionality that was present when i bought the product. I'm not sure this is legal.
This is also easily solvable. Let users with a ru key bought up to today play with the language they please.