Linguistic and Cultural Competences are closely linked, as they involve the ability to infer and trace truths within knowledge stored in memory. Humans respond to three interrelated questions: Logic, Epistemology, and Ontology. This paper defines a place for Cultural Competence within these philosophies through Epistemic Modal Logic and Dynamic Possible Worlds. Cultural Competence is crucial in social robots: pleasantness goes with it, but it also has practical functions, managing incomplete pieces of knowledge and shortening the customisation. The artificial agent simulates empathy and meta-cognition, enacting justified action plans that conform with ontology and its awareness thanks to the Euclidean S5 accessibility relation between possible worlds.