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.
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.
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).
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).