To open registry (if you don't know how): how to
for win 7 - same as for Vista.
Then registry editor will open, and you'll see five keys:
You need to choose "HKEY_LOCAL_MACHINE" first, then "SOFTWARE", then "Ubisoft" and then click on "Might & Magic Heroes VI". You need to click not on the triangle here, like for the first 3 steps, but on the text.
Next, in the right part of the window, you'll see some values. You need value named "language". Double click on it, and then type "409". Next, press enter, or click on "OK". That's all. This should work, but I'm not sure that Russian version has English in it as well.
And... You are Russian, right? I can explain it in Russian, if it helps.