February 21st marks UNESCO’s International Mother Language Day. IMLD has been observed yearly since February 2000 to promote linguistic and cultural diversity and multilingualism.
IMLD originated as the international recognition of Bangladesh’s Language Movement Day, which has been commemorated in Bangladesh since 1952 following government attempts in 1948 to make Urdu the sole national language and thereby angering the Bengali-speaking majority of East Pakistan. Anger and discontent peaked in 1952 when protesting students at the University of Dhaka were killed at a protest on 21 February.
Bengali was recognised as the second official language of Pakistan on February 29, 1956, and the constitution of Pakistan was reworded to “The state language of Pakistan shall be Urdu and Bengali.”
For more on the topic of the Bengali Language Movement, the 2008 book State language movement in East Bengal, 1947-1956 by A.M.A Muhith takes a comprehensive look at the issues. Tariq Rahman’s Language and politics in Pakistan (1996) looks at other political and cultural aspects of language in Pakistan,with chapters on British Language Policies and Imperialism; Pashto Language Movement; Urdu-Hindi Controversy; Language Movements of Balochistan, and more. Both of these titles are available at Koerner Library.
If you just want a summary, the Wikipedia entry on the Bangladesh Language Movement provides a good starting point; check out the list of citations at the end for more articles, newspaper reports, and more.