February 21 is Language Martyrs' Day in Bangladesh, and International Mother Language Day by proclamation of UNESCO (the United Nations Educational, Scientific, and Cultural Organization).
Language Martyrs' Day (also known as Shahid Dibas or Ekushey) commemorates the demonstrators who died in the effort to have the Bengali language recognized (alongside Urdu) as an official language of East Pakistan (now Bangladesh). On February 21, 1952, a large group of protesters gathered in Dhaka to urge the Pakistani government to recognize their language. The organizers of the prostest were students at the University of Dhaka, but the protesters were from all walks of life. The protesters were fired on by the police, and many were killed. However, the proponents of Bengali language rights ultimately prevailed. When Bangladesh became independent in 1971, Language Martyrs' Day became a national holiday.
In November 1999, a general conference of UNESCO declared February 21 to be International Mother Language Day. Although the new holiday is intended to honour linguistic diversity in general, and to promote language preservation among the member nations, the date was selected in memory of the Bengali language martyrs. International Mother Language Day was first celebrated on February 21, 2000; among the celebrants were Koïchiro Matsuura (UNESCO's Director-General) and Vigdís Finnbogadóttir (the former president of Iceland, and UNESCO's Goodwill Ambassador for Languages).