The lingua franca of porn has to be English. Due to the overwhelmingly US bias of pornography, even that produced elsewhere tends to be promoted in English and appear on sites that are either wholly in English or navigable by an English speaker.
It’s rare to find exclusively non-English porn sites. This is partly due to laws in much of the world prohibiting the production, distribution, storage and viewing of porn but for the most part is because the Internet started in the US and the US pornographers were early adopters.
It’s therefore common for non-English speakers to be able to understand English, especially US English, sexual slang but not the other way round.
Take Félix Faure his infamous “pompe funèbre” is legendary. Never heard about it? Well he was French president 1895 to 1899 and died (if the scurrilous rumours are to be believed) in his office receiving a blowjob from his secretary Marguerite Steinheil. In French the verb “pompe” means both “to pump” and to give oral sex to a man therefore “funeral pump”.