<p>Research in Latin America has made significant advances in multilingual approaches to mathematics education, yet this work remains underrepresented in researcher education. To address this gap, we explored how Master’s courses enable student-researchers to design Multilingual Instructional Resources for mathematics teaching in indigenous schools. Using an intrinsic case study, we examined a three-course sequence in a research-based Master’s program in Mexico, developed in the <i>Questioning the World Paradigm</i>. Across the sequence, each course established, and progressively enriched, didactic milieus by integrating three essential dimensions: mathematical, cultural, and linguistic. Through a media-milieu study dialectic we analyze how media like academic papers and educational resources focused on indigenous education shaped –and were shaped by– the evolving milieus to support the design, implementation, and evaluation of bilingual (Otomi-Spanish) instructional resources. Two resources created by a student-researcher, Atl, are presented. Implemented in Otomi classes, they engaged pupils in a new teaching approach framed by two fundamental mathematical activities: counting, through explorations of Otomi numbers and their arithmetic composition; and designing, through a spatial structuring task related to manufacturing objects. Cultural dimensions are promoted through co-design with indigenous teachers to explore Otomi mathematical meanings, while linguistic dimensions are established through the explicit use of different languages. Findings highlight how Master’s level researcher education can cultivate inquiry, co-design, and bilingual implementation practices to contribute to revitalizing indigenous languages through mathematics education.</p>