This article examines how digital platform infrastructures restructure multilingual ecologies in frontier regions, using Hainan Island as a case study. Historically, Hainan sustained a layered multilingual equilibrium in which Hlai (Li), Hainanese (Southern Min), and Mandarin occupied differentiated social domains. Functional specialization and spatial segmentation enabled asymmetrical yet stable coexistence without large-scale structural convergence. However, the rise of digitally mediated communication introduces a qualitatively distinct organizing principle. Rather than distributing linguistic authority across socially negotiated domains, digital platforms centralize visibility through interface design, algorithmic amplification, and technological standardization. Drawing on sociolinguistic scaling theory and platform studies, this study proposes the Digital Multilingual Ecological Shift Model (DMESM), which conceptualizes the transition from domain-based equilibrium to platform-induced hierarchy. The analysis demonstrates that minority languages such as Hlai face cumulative infrastructural constraints, including limited orthographic standardization, lack of input system integration, and reduced algorithmic visibility. As governance, commerce, and education increasingly migrate online, linguistic vitality becomes dependent not only on intergenerational transmission but on infrastructural embedding. The findings suggest that digitalization constitutes structural ecological reordering rather than communicative expansion. The model offers a framework for analyzing digitally mediated multilingual inequality beyond the Hainan context and contributes to the theoretical extension of contact linguistics into the era of platform governance.