"International Mother Language Day was proclaimed by the General Conference of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in November 1999 (30C/62).

On 16 May 2009 the United Nations General Assembly in its resolution A/RES/61/266 called upon Member States "to promote the preservation and protection of all languages used by peoples of the world". By the same resolution, the General Assembly proclaimed 2008 as the International Year of Languages, to promote unity in diversity and international understanding, through multilingualism and multiculturalism."
International Mother Language Day

The United Nations website notes that "[International Mother Language Day] represents the day in 1952 when students demonstrating for recognition of their language, Bangla, as one of the two national languages of the then Pakistan, were shot and killed by police in Dhaka, the capital of what is now Bangladesh."