A social organization in which diversity of racial or religious or ethnic or cultural groups is tolerated WordNet 3.0 & Open English WordNet

Cultural pluralism is a term used when smaller groups within a larger society maintain their unique cultural identities, whereby their values and practices are accepted by the dominant culture, provided such are consistent with the laws and values of the wider society. Wikipedia

A social system that permits smaller groups within a society to maintain their individual cultural identities. Wiktionary