The core Invaders aren't an especially "international" group; there's a bunch of Americans (counting the Torch), an Atlantean who they don't have the rights to, and two Brits.
Union Jack is the most obvious choice for inclusion (I'd like them to allude to Lord Jack's WWI exploits as an inspiration for both Cap and the Skull). No one here has mentioned Spitfire, though, the other international member; she has what is probably the most "out-there" powerset of the characters mentioned, but she's also a woman, which probably counts in her favour, given the limited opportunities for female roles in this movie.