The official language of Bangladesh is Modern Standard Bengali (Literary Bengali). It serves as the lingua franca of the nation, with 98% of Bangladeshis fluent in Standard Bengali or Bengali dialects as their first language. Chittagonian: spoken in the city of Chittagong and in much of the southeast of the country, it is often considered to be a dialect of Bengali, but both languages are mutually unintelligible to each other. 2  Hajong: originally a Tibeto-Burman language that has shifted over time to an Indic language.