Language doesn't matter, because always sooner than later, couples create their own. After some time you can tell when that lost look in the morning means he run out of clean underwear, you know what he is going to order in the restaurant, and the moment he calls you can answer "so, you are late, aren't you?" and you can tell what he is going to say next. And how he is going to say it. And in which language.

Language doesn't matter, but it matters so much. Your own particular language. The words you say with your eyes, and your gestures and with everything you do. Because after some time, you not only know but you expect that he knows. That he understands your smile or your lack of it. And knows what to say next. And how to say it. And in what language. And if he doesn't, well, that's is a real communication problem.