Jürgen Vogel has two appearances in the film. First he has a cameo as one of the arrested protesters (in the front row, wearing a blue jacket) and later he appears as the chicken in the supermarket (a reference to Wolfgang Becker's earlier film Life is All You Get) for which he is credited as "Das Küken" ("young chicken").
CGI was used extensively to "de-Westernize" Berlin. Even though it's mostly shot in the former East Berlin and much of the film takes place after the fall of the wall, it's been Westernized since at a furious rate. Many ads for Western products had to be removed, and many colors had to be lightened or grayed significantly.
The reason Dennis is seen wearing a T-shirt that resembles the computer code from The Matrix is because there was initially a scene where he talked about a movie idea of his called "Planet of the Forgotten" which bore a striking resemblance to the plot of The Matrix. This scene can be viewed in the deleted scenes of the DVD.
Sigmund Jähn gave permission to be featured in the movie, but refused to play himself. It was very difficult to find an actor who looked like Jähn and spoke his typical dialect but after filming had begun, Wolfgang Becker chose Swiss actor Stefan Walz. He was given complex make-up and was dubbed by another actor who came from Jähn's home region, the Vogtland.
As Chulpan Khamatova did not speak enough German to improvise properly, she had to learn her (grammatically correct) sentences word for word. Because this did not sound natural, all of her phrases were translated into Russian and then translated back word for word to get a natural Russian accent with all typical grammar mistakes.
At the birthday party when Rainer tries to hide from Christiane his West German origin, he almost says he was a Gauleiter in the children's Pioneer movement. A Gauleiter was the name given to a regional Nazi party leader.
The story is loosely based on the last two years of V.I. Lenin's life, living in a controlled environment similar to what is portrayed in the film. With the justification that over-excitement might cause Lenin health problems, Joseph Stalin had printed for him one-copy edition newspapers, censored of all news about the political struggles of the time.
The helicopter that flies past Alex' mother carrying a statue of Lenin is a Mil Mi-8 transport helicopter that was widely used in all Warsaw Pact states. In the GDR it was used specifically in the role of a flying crane.