The role of multilingual proficiency dynamics in code-switching frequency across two countries and three generations: evidence from immigrant self-reports

Few immigrant communities manage two heritage languages (HLs) alongside a dominant societal language (SL) across generations. The present study examines how language proficiency dynamics shape code-switching (CS) frequency among three generations of Mountain Jews (MJs) in Israel and the United States. Having immigrated from across the eastern Caucasus throughout the 1990s, MJs brought two HLs–Juhuri (Judeo-Tat), an endangered Jewish language, and Russian, the SL of their country of origin–into contact with the local SLs, Hebrew and English. Drawing on self-reported data, the study revealed a generational decline in HL proficiency, particularly in Juhuri, and rising dominance of the SLs in both countries. CS occurred most frequently between Russian and the SL, and least between Juhuri and the SL. Regression analyses show that while CS is generally linked to higher proficiency in the HLs involved, a consistent pattern emerged: proficiency in a third, adjacent language not involved in switching negatively predicted CS between the other two. This pattern reflects interlinguistic competition across multilingual repertoires. Comparisons between countries highlight how cultural environment and sociolinguistic context may mediate this effect, offering new insights into the complexity of HL use, maintenance and shift among understudied groups of multilingual immigrants.