Since all of the english sounds should have german/russian counterparts (that the enemy team hears), this shouldn't be too hard to just mod.
The enemy speaks the native tongue, but that isn't the full 3000 lines iirc.
So the game loads the english 3000 lines and the smaller bunch of enemy rusky/german lines.
So when you mod them around you have actually less battlechatter.
But I agree with Darkseed; Although I am terrible at russian, german is fine for me, so I would love to have the option to do that.
However Alan explained why they did it this way and I just hope that they find the time to add it in later