From the United Nations website: Human Rights Day:
"Human Rights Day is observed every year on 10 December — the day the United Nations General Assembly adopted, in 1948, the Universal Declaration of Human Rights (UDHR). The UDHR is a milestone document, which proclaims the inalienable rights that everyone is entitled to as a human being - regardless of race, colour, religion, sex, language, political or other opinion, national or social origin, property, birth or other status. Available in more than 500 languages, it is the most translated document in the world".
Since the adoption of the Universal Declaration of Human Rights on December 10, 1948; the month of December has been traditionally recognized as Universal Human Rights Month.