Indeed. If I remember correctly, the author was a relationship/marriage counselor and he witnessed many failing relationships where the partners really loved each other, they just didn't use the right channels to express it to each other. By saying that different people have different ways how they can best express (and best receive/understand/accept) love, and if they don't understand what kind of love the other one needs (and can understand) the most, it's like not knowing the language of each other, it's not too far-fetched to use the word "language" in this context.