Alice, I am afraid, there couldn't be any good cooperation and trust
between ATC and pilots, because from the very beginning the pilot
knew, he will be trying to land, but was lying to the ATC, that he won't.
The other problem was, that normally, in a Russian crew
AFAIK it would be the
navigator (shturman) who would be talking to the tower, and the pilot
would be just flying, not talking.
As you noticed, from the moment they contacted Smoleńsk tower the
navigator asked: "Are we going to talk Russian?", when the PIC answered "yes"
he also took over all the communication with the ATC from navigator.
So, from this point of view, we can assume the navigator couldn't speak Russian,
on the other hand the PIC was too busy with other activities to read back the altitudes.
In this respect the ATC was correct in his assumption:
"They probably didn't know Russian language."
The navigator obviously didn't, the only communication he did before
was in English.
You can ask your colleagues on the forum, who in the crew is
normally reading back to the ATC? I know it just from hearing.