Small talk

Mon interlocuteur venait du même service is an ordinary French sentence, the kind somebody says at a coffee machine, and it cannot cross into English on the word that looks ready for it. « Interlocutor » exists, and a dictionary will offer it, but nobody says it. Where it is alive at all it is diplomatic or legal: « the government has no credible interlocutor » means a counterpart fit to negotiate with, not simply whoever happens to be speaking. Used of a colleague at a conference it sounds like the transcript of a hearing. French has no such trouble: l’interlocuteur is neutral and very common — changer d’interlocuteur, je n’ai pas eu le bon interlocuteur, regarder son interlocuteur dans les yeux. English has no everyday noun for that role, so it rebuilds the sentence around a relative clause — « the person I was talking to », « whoever picks up the phone », « the other person » — or drops the role and names the human being: « the man I was speaking to came from the same department ». The gap is worth knowing: the French noun names a role that English can only describe.