The credits spell the character's name as "Van Aken". Likewise the street name is "Van Aken". However, when we first see the residence, the caption reads, "Van Aiken residence". The spelling is also 'Van Aken' on the front page of the newspaper Segal puts on the counter of the hotel's reception when checking in.
After the white-haired villain is shot through a window, he survives and pulls guns from his metal case. He puts a cigarette to his mouth which briefly disappears when he cocks his gun.
When Dunoir enters the hotel room where Mr. Mimms is checked in under Cold's name, he is holding two handguns. The handgun in his right hand has a silencer on the end of the barrel. However, when he fires from both handguns into the shower, no silencer is seen on the gun in his right hand, and loud gunshots are heard. When he turns in the next camera shot, the silencer is back.
German ZIP codes have five digits, not four as seen on the note.
The type of license plate (B-12345) Mrs. Van Aken's car has is reserved for administrative (like police/fire department or ambulance) and government vehicles. Normal plates look like B-AB 1234.
There is a big sign right beside the main entrance of the train station which reads "Achtung! Stromleitung!" ("Attention! Electric line!"). It is highly unlikely that such a sign would be there because either the line is wired in a way it doesn't harm people or it wouldn't be there at all (due to the vast amount of security protocols and rules concerning electricity in Germany).
A white 737 is shown landing in what is supposed to be Berlin. The 737 is actually an Alaska Airlines 737. You can clearly see the Alaska Air Eskimo on the tail. Alaska does not fly to Europe.
In the scene where the characters exit the burning farmhouse, Steven Segal's stand-in is clearly visible.
During the fight between Dunoir and Cold at the end of the movie, the knife Dunoir pulls is clearly a rubber training knife (note how it wobbles side to side during the slow motion portions; it is also uncharacteristically thick).