International Mother Language Day observed every on:

A. 15 February

B. 17 February

C. 21 February

D. 24 February

Details: 

International Mother Language Day is a worldwide annual observance held on 21 February to promote awareness of linguistic and cultural diversity and to promote multilingualism. First announced by UNESCO on 17 November 1999, it was formally recognized by the United Nations General Assembly with the adoption of UN resolution 56/262 in 2002.