Hanna doesn't understand the ritual she's seeing in the cathedral scene but she connects to the music, because, as writer-producer David Farr puts it, "Art is the one thing that we all instinctively have in common."
Actor Khalid Abdalla, who plays Jerome Sawyer, is a graduate of Cambridge University and is fluent in three languages: English, French and Arabic. He was born in Glasgow, Scotland, to Egyptian parents.
The church that Hanna wanders into in episode 4 is not in Berlin. It's actually in Budapest. There are no baroque churches of that nature in Berlin... especially in Kreuzberg.
Berlin has a rich cinematic tradition, including the first film screening for a paying audience, at the Variete Wintergarden in 1895.
The sequence of Hanna wandering around the Kreuzberg borough of Berlin was almost cut five times, because very little of it was specifically required for the story.