This working paper develops an ideal-type theoretical framework for analyzing institutional language change through mechanisms of norm diffusion. Existing explanations of linguistic change typically emphasize either decentralized cultural evolution or explicit state-directed language planning. This paper proposes a complementary model describing how administrative, professional, and organizational incentives may facilitate the diffusion of linguistic norms within institutional settings. The framework identifies five sequential stages—Institutional Access, Resource Mobilization, Norm Diffusion, Coalition Reinforcement, and Norm Enforcement—and integrates concepts from sociolinguistics, institutional sociology, social psychology, political science, and administrative law. It distinguishes between coordinated and emergent forms of institutional language steering, specifies explicit boundary conditions and failure modes, and proposes empirical methods for evaluating the model using corpus linguistics, organizational documentation, and legal case analysis. The paper is intended as an analytical framework rather than an account of any single historical or contemporary case. It advances a falsifiable model for investigating how linguistic norms may develop, stabilize, or reverse within formal institutional environments.