In the case of Rocco Siffredi, who's apparently an Italian, the only excuse is just that (he's Italian). Italian is a Romance language, which is a branch of the Indo-European language family, just like Germanic languages. This means that the grammar is still, for a large part similar or even the same, but what if a Hungarian (or Finnish, but I don't know that many) adult performer joined? Would you guys make fun of that as well? Hungarian is an Uralic (or more specific Ugric) language and isn't related to the Indo-European languages at all. This means that even the simplest rule in the language is different (that includes, but is not limited to grammar).
Of course the accents are funny. So is mine & I'm a dutchman... This means I could swim to England if I wanted to (which I don't btw!), and I'm not bothered by my accent at all, but I do hope that everyone here has enough common sense that if an Hungarian girl joins who has not perfected her English yet (& maybe never will), who'll probably make some errors when it comes to grammar, etc (more than the other posters here), that other people won't immediately bash her or make fun of her...