The Ethno-Linguistic Fragmentation index aims to measure the probability of two random individuals belonging to the same group. However, a person may belong to several groups; therefore, the Pluri-Ethno-Linguistic Fragmentation index generalizes the ELF index to consider multiple belongings within a country. PEL index results are discussed in relation to the crucial case of Luxemburg, which provides evidence of the validity of our new proposed index. The PELF index deepens our understanding of the repercussions of the coexistence of several languages in a society.