How much of this is true? Probably most of it, or at least it's told as well as Berenshtein himself knew how to tell it.
A story during WW2 of Russian resistance against the German onslaught, with Berenshtein apparently in a few quandaries, one of which is whether or not to even reveal his real name.
The story is ultra confusing. And it's hard to understand the dialog. It's dubbed in English, and without subtitles, you really can't understand more than a few words by any actor other than the main character.
Still, you do get a "feel" for what is going on. It's just confusing. There is a commander over Berenshtein, but he is also a leader of what seems to be a squad.
One command character parachutes in early and gives Berenshtein's commander some static about his role in the war. They're supposed to cover for thousands of troops crossing a river.
Berenshtein is part of an intelligence unit, and the plot jumps into the future without explanation often. At one point, although they are lacking in food, Berenshtein is at a dinner for officers, and one of them angers him, but I have no idea what the anger is from. He invites the officer outside and hits the officer, and then nothing else happens from this incident.
Later, he parachutes with his squad into a place further West, landing in Poland, where he doesn't want to be. We're led to believe he's a hundred miles from his destination, then we hear him say he's two miles away, so again there is confusion.
The squad learns of a German super weapon that sounds like something Captain America would run into, and their plans change. Their plans change again to do a humanitarian effort. Do they get back to the Captain America plan? I won't tell you.
I think the point here is that everyone is confused in the war, and that's okay, because that's the point of the movie I think.