Abstract
This study investigates the role of language as a social function and identity marker within the framework of volunteer service education at universities in China and Kazakhstan. Set against the backdrop of the United Nations' Sustainable Development Goals (SDGs), particularly SDG 4 (Quality Education), SDG 10 (Reduced Inequality), and SDG 17 (Partnerships for the Goals), the research explores how sociolinguistic approaches can illuminate the intersection between language use and identity formation among university student volunteers. By employing comparative case study methodology and drawing on survey and interview data, the study identifies both convergences and divergences in how volunteer participants in China and Kazakhstan experience and negotiate their social roles through language. Language not only mediates communication but also serves as a means of identity building and intercultural comprehension embedded within the framework of global citizenry that falls within the SDG global citizenship agenda. In both countries, the use of multiple languages—especially English and national/local languages— played a pivotal role in shaping volunteers' perceptions of themselves and others. The sociolinguistic analysis further reveals that the institutional context and national language policies significantly influence students' linguistic behavior and their perceived identity in volunteer roles. The present study contributes to this debate through its argument for the application of a sociolinguistic approach in service learning programs offered in universities. It provides policy and pedagogical guidelines on creating more inclusive, culturally sensitive, and linguistically competent volunteer programs that meet the Sustainable Development Goals at the global level.