Ethnic language is a core component of cultural identity and plays a vital role in shaping self-esteem and psychological well-being in multilingual societies. This study aimed to develop and psychometrically validate the Ethnolinguistic Identity Scale (ELIS) and examine its relationship with self-esteem among Iranian university students. A descriptive cross-sectional design was employed, with 690 students recruited through online convenience sampling. Data were collected using the newly developed 25-item Ethnolinguistic Identity Scale and a standardized measure of self-esteem. Exploratory factor analysis identified five dimensions—ethnolinguistic knowledge, ethnolinguistic belonging, ethnolinguistic self-esteem, ethnolinguistic language use, and ethnolinguistic language maintenance and transmission—which together accounted for approximately 79/86% of the total variance. Confirmatory factor analysis supported a good model fit. Reliability was established through Cronbach’s alpha (0.91), composite reliability (0.95), and test–retest reliability (0.76). Furthermore, concurrent validity was supported by a significant positive correlation with self-esteem, while known-groups validity was demonstrated by the scale’s ability to differentiate between varying levels of ethnic language use. Overall, the findings indicate that the Ethnolinguistic Identity Scale is a multidimensional instrument with robust psychometric properties, suitable for application in psychological and cultural research and interventions. Additionally, ethnolinguistic identity is associated with higher levels of self-esteem among students in multilingual societies and may help explain individual differences in self-esteem.