In the dialects prevalent in much of eastern and south-eastern Bangladesh (Barisal, Chittagong, Dhaka and Sylhet Divisions of Bangladesh), many of the stops and affricates heard in West Bengal are pronounced as fricatives. Linguist Suniti Kumar Chattopadhyay grouped these dialects into four large clusters-Rarh, Banga, Kamarupa and Varendra but many alternative grouping schemes have also been proposed. The south-western dialects (Rarh or Nadia dialect) form the basis of modern standard colloquial Bengali.
Regional variation in spoken Bengali constitutes a dialect continuum. Language is an important element of Bengali identity and binds together a culturally diverse region. In 1999, UNESCO recognized 21 February as International Mother Language Day in recognition of the language movement in East Pakistan (now Bangladesh). Furthermore, it is believed by many that the national anthem of Sri Lanka (Sri Lanka Matha) was inspired by a Bengali poem written by Rabindranath Tagore,while some even believe the anthem was originally written in Bengali and then translated into Sinhalese. In 1952, the Bengali Language Movement successfully pushed for the language's official status in the Dominion of Pakistan.
The first two verses of a patriotic song written in Bengali by Bankim Chandra Chatterjee, Vande Mataram, was adopted as the "national song" of India in both the colonial period and later in 1950 in independent India. Both the national anthems of Bangladesh ( Amar Sonar Bangla) and India ( Jana Gana Mana) were composed in Bengali by Rabindranath Tagore. Bengali literature, with its millennium-old history and folk heritage, has extensively developed since the Bengali renaissance and is one of the most prominent and diverse literary traditions in Asia.