This study examined language-choice patterns, code-mixing, code-switching, and domain contraction within the multilingual ecology of Universitas Alkhairaat Palu, and considered their implications for Indonesian academic-language instruction. A qualitative ethnographic case study was conducted from February to July 2026 with 18 purposively selected participants (4 lecturers, 4 educational staff, and 10 students). Data were generated through participant observation, structured in-depth interviews, and institutional document analysis across academic, administrative, religious-ceremonial, and informal domains. Analysis combined iterative data reduction, domain-based coding, data display, conclusion drawing, and verification; credibility was supported through source, method, and theory triangulation and reflective field notes. Indonesian remained the principal academic and administrative language, while Arabic appeared systematically as a marker of religious authority and institutional identity. English was used mainly in informal peer interaction, whereas Kaili showed the narrowest functional distribution and was often limited to lexical fragments. These patterns indicate an unequal institutional language hierarchy rather than a measured longitudinal shift. A four-meeting Problem-Based Learning and directed-translanguaging prototype was derived from the findings as a preliminary pedagogical proposal; its effectiveness was not tested in this study.