The sequel was considered months before The Expendables (2010) was completed and released in theaters. The first movie's plot was revised during filming so that Dolph Lundgren's character, who was killed in the first draft, could be saved for the sequel.
Sylvester Stallone asked Chuck Norris to include a reference to The Chuck Norris facts (a popular internet meme) in the screenplay. Norris's wife Gena O'Kelly suggested him the one with the cobra. ("Chuck Norris was bitten by a cobra, and after five days of excruciating pain... the cobra died.")
The film reveals that Gunnar Jensen (Dolph Lundgren) has an advance degree of chemical engineering. This is a reference to Lundgren himself, who has a degree in chemistry from Washington State University in 1976, a degree in chemical engineering from the Royal Institute of Technology in Stockholm in the early 1980s, then a Master's Degree in Chemical Engineering from the University of Sydney in Sydney in 1982. The character abandoned his career a scientist to work as bouncer in order to impress a girl. In real life, Lundgren turned it down to work as bodyguard for his then girlfriend Grace Jones. Further, while stuck in the mine Gunnar refers to himself as a "Fulbright Scholar" which Lundgren also achieved in real life.
Sylvester Stallone explained that his casting was looking particularly for actors who had not experienced recent hits: "I like using people that had a moment and then maybe have fallen on some hard times and give them another shot. I like those kinds of guys. Someone did it for me and I like to see if I can do it for them."
In the battle scene with all the Expendables and the Sangs there are many tongue-in-cheek references to the actors other films such as Arnold Schwarzenegger and Bruce Willis saying "I'll be back" (many of Arnold Schwarzenegger); Arnold Schwarzenegger saying "Yippie-Kai-Yay" (in reference to Bruce Willis "Die Hard" series) and later asking "Who's next, Rambo?" (Stallone's film).
Some controversy arose online when rumors started spreading that this film might receive a PG-13 cut, as opposed to the Rated-R cut of the first The Expendables (2010). The name of Chuck Norris was most often associated with this story, that he was having problems with the extreme violence and basically refusing to take part in the movie unless it would be toned down. In this context it may be worth noting that, while his character does kill a great deal of people, the film never directly shows him doing any of it.
In an interview with BBC Radio, Sylvester Stallone confirmed that he named Jean-Claude Van Damme's character 'Vilain' to make it similar to the name of 19th Century French poet Paul Verlaine. This was to set up an extremely obscure in-joke where the final showdown between Van Damme and Stallone, could be seen as a fight between Vilain/Verlaine and Rambo/Rimbaud. Arthur Rimbaud (pronounced Rambo) being another French poet with whom Verlaine had a tempestuous affair.
Chuck Norris is the pop culture subject of countless larger than life "Chuck Norris facts" created by fans. The film's cast and crew jumped on the bandwagon when Norris arrived in Bulgaria, coining a new one: "Chuck Norris doesn't visit Bulgaria, Bulgaria visits Chuck Norris."
The fountain pen that Barney Ross pulls out to write on the napkin is a Montegrappa Chaos limited edition pen that Sylvester Stallone, a long time Montegrappa aficionado, helped design. It includes a skull and other symbols inspired by The Expendables (2010).
Sylvester Stallone's character is named Barney Ross in memory of decorated WWII hero and World Lightweight, Light Welterweight, and Welterweight Boxing Champion, Barney Ross (i.e. three-divisional champion).
The trivia items below may give away important plot points.
The working storyline had Mickey Rourke from The Expendables (2010) returning as Tool and being killed off as the motivation for the team's subsequent actions. This was changed to Liam Hemsworth's character when Rourke abruptly left the production to pursue another project.