In multilingual education for sustainable personal development, compared with that of multiple languages, the teaching and learning of multiple varieties of a language has been underexplored as a special and important form of multilingualism. In this article, we examine the linguistic, psychological, and social characteristics of multiple variety learning, as compared with multiple language learning. Linguistically, acquisition of language varieties is a process of assimilating variants from a new variety into an earlier variety, which serves as a prototype system. Such assimilation is a psychological project of form-meaning interface development, which may follow the patterns of structural multiplication, conceptual involution, conceptual evolution, or/and conceptual transfer. When multiple language varieties are actually used in social contexts, multilingual individuals’ selected language practices may be supported by their combined linguistic resources from multiple varieties rather than depend on a single variety despite its dominance in a given situation. These characteristics carry pedagogical implications for sustainable multilingual education, particularly for the teaching and learning of foreign languages that have multiple varieties.