Maintaining the First Language and L2 Speaking Performance: Evidence From Lexical Diversity, Fluency, and Syntactic Complexity

This study examined whether maintaining the first language (L1) or experiencing dominant language shift affects second-language (L2) speaking proficiency. Twenty-four Russian-English bilinguals were divided into a bilingual maintenance group and a dominant language shift group based on self-reported L1 proficiency. To avoid monolingual bias, all comparisons were made between bilingual speakers. Participants produced spontaneous narrative speech using picture books, and their L2 output was analyzed for fluency, lexical diversity, and syntactic complexity. Across all measures, no statistically significant differences emerged between the groups. Individuals who maintained their L1 performed similarly to those who had lost their L1, indicating that continued engagement with the L1 does not impede L2 oral development. Maintaining the L1 did not yield any measurable benefits, as these participants did not perform better than those in the dominant language shift group. These findings contribute to a more nuanced, domain- and usage-specific understanding of the linguistic interdependence hypothesis and the common underlying proficiency model, indicating that although L1 maintenance does not impede L2 performance, L1 loss may not compromise the development of everyday L2 speech.