Meryl Streep not only learned a Polish accent but also learned how to speak German and Polish in order to have the proper accent of a Polish refugee. She reportedly learned Polish from one of the assistants working on the film who happened to speak it.
Meryl Streep's performance as Sophie Zawistowska is ranked #3 on Premiere Magazine's 100 Greatest Performances of All Time.
Meryl Streep begged director Alan J. Pakula for this role literally on her hands and knees. Marthe Keller and Barbra Streisand both tried to win the role also, but Pakula ultimately chose Streep.
In a disclaimer paragraph at the end, the only character who was not fictitious was Rudolf Hoess, which was the name of the actual commandant at Auschwitz.
After seeing him in this film, John Cleese decided to cast Kevin Kline in his movie Un pesce di nome Wanda (1988).