The United Nations proclaimed 21 June as:

The United Nations proclaimed 21 June as:

International Mother Language Day
International Widows' Day
International Day of Yoga
International Day against Drug Abuse and Illicit Trafficking
This question was previously asked in
UPSC NDA-2 – 2016
The United Nations General Assembly, by resolution 69/131 adopted on 11 December 2014, proclaimed 21 June as the International Day of Yoga. The initiative was proposed by India and supported by a large number of member states.
International Days are designated by the United Nations to mark particular events or topics, in order to promote awareness and action. These days serve as a way to focus global attention on important issues.
Other dates mentioned: International Mother Language Day is February 21; International Widows’ Day is June 23; International Day against Drug Abuse and Illicit Trafficking is June 26.