love languages are applicable to more than just Christians. The book “The Five Love Languages” is written by a Christian man and from a Christian standpoint, but the theories therein are applicable fore non-Christians. It simply outlines a model for communication of love: how it is expressed vs. how it is received, and how people generally fall into five different categories of how they prefer to receive love (quality time, gifts, words of affirmation, physical touch, and [another one I can’t remember]) for the purpose of aiding a marriage relationship.
Many people can quickly identify their love language and sometimes are able to identify that of others, and act accordingly to improve relationships (e.g. I became much more tolerant of my father’s seeming inability to express love to me when I realized that my love language is quality time [specifically, conversation] and that despite this I wasn’t very tolerant of conversation with him when it came).