As Rone is driving the taxi away at about 95 minutes in, the Helsinki filming locations are revealed as overhead signs for a Finnish business (part of the word "kansallis-" meaning "national") are partly but not fully covered by signs in Russian.
When The Whore and Rone each visit Kitai at the hospital, they are told by the desk attendant to take the third door down the corridor in Russian. Both then enter through the first door on the right instead.
When Ward and the Whore talk in the bathroom at the end, the movie crew is reflected in the tiles.
The icebreaker drops them off in the frozen Kara Sea. Later Colonel Kosnov says, "Goddamn fools! Trying to come in through Vorkuta." Vorkuta is over 100 miles inland from the Kara Sea.
When Rone asks the man on the street to give him a light for his cigarette, just before the Warlock jumps to his death, he is holding the cigarette backwards and putting the tobacco to his mouth. Russian cigarettes have/had very little tobacco and a very long filter end. You can see this in earlier scenes with people smoking cigarettes.