The gun used to kill Krug has a silencer attached. However, in the flashback sequence (during the conversation between Burkhardt and Renard) it has the sound effect of a non-silenced gun.
The lines "Ich warte auf ihn jetzt" and "Hier kommt er", as spoken by Krug, are translated literally from English. Both lines are not used in that way by German people.
When Adalind leaves her mother's house, you can hear the door closing and the lock snapping into place. However, when you look closely, the door swings slightly back, meaning it wasn't locked at all.