What facilitates diffusion and political interaction between culture groups?

Language

Polyglots

Accents

Place names

The correct answer is: "language".

Language is the basis of communication and proper understanding of each other when groups with different political, cultural or social backgrounds are interacting. For example, a polyglot, which is a person who speaks several languages, would be only useful in the case that he finds another person in the other cultural group, who speaks one of those languages. Therefore, the language is the clue.