This paper critically examines Ishwar Chandra Vidyasagar's philosophy of language and its implications for contemporary teacher education through the framework of vernacular epistemologies in postcolonial settings. The central argument is that Vidyasagar's promotion of Bengali as a medium of instruction was not merely a pedagogical preference but a deliberate epistemological intervention—an early form of what decolonial scholars now term epistemic decolonisation. Drawing on primary textual analysis of Barnaparichay (1855) and Vidyasagar's educational writings, alongside sociocultural theory (Vygotsky), decolonial thought (Mignolo; de Sousa Santos), and indigenous knowledge frameworks (Battiste), the paper demonstrates how vernacular language functions as a mediational tool in knowledge construction rather than a neutral communicative vehicle. The analysis reveals three core contributions: vernacular epistemologies as mechanisms of epistemic resistance; the teacher as a cultural and epistemic mediator; and the structural tensions between vernacular education and globalisation. Crucially, the paper also problematises the romanticisation of vernacular approaches, cautioning that uncritical adoption can reproduce internal social hierarchies. The paper concludes with a pluralistic, multilingual model for teacher education that is contextually grounded, epistemically just, and globally competent.