21st Feb is a day for Bangladeshis to celebrate their culture, traditions and their Bengali national language. Bangladesh is the only Nation who had to fight for the right to their mother tongue.
The date represents the day 21st February 1952 when four young students were killed in Dhaka, the capital of Bangladesh, during a protest march because of Bengali language controversy that happened due to partictaion of India and East Bengal being annexed as part of Pakistan.
Over time the day became know as Shaeeds day or Martyrs day, and in 1999 UNESCO adopted 21st February as the International Mother Tongue Day.
The day is Dhaka and in places around the world where a Shaheed Minar is members of community would gather and lay wreaths and remember the 4 students that fell to protect the mother tongue language of Bangla. To find out more visit teh unesco site here https://en.unesco.org/commemorations/motherlanguageday