The term "gay train" is a pornographic term used to describe a specific type of sexual activity among gay men, where one man performs oral sex on another man's penis while the second man anally penetrates a third man. This creates a train-like formation, with one person at the "front," performing oral sex, and two others behind them engaging in anal intercourse. The term "gay" indicates that the participants are men attracted to other men.
In this context, "gay" is used as an adjective to describe the type of sexual activity involved - specifically, a same-sex encounter between men. It doesn't mean that the video itself is in a non-English language or contains any specific cultural references from a country where gay relationships are more openly accepted and celebrated (e.g., certain parts of Europe or North America). It simply implies that the content involves male-on-male sexual activity.