Democracy is a human right, and is as such, included in a number of the most important international human rights standards, such as the Universal Declaration, art. 21:
1. Everyone has the right to take part in the government of his country, directly or through freely chosen representatives … 3. The will of the people shall be the basis of the authority of government; this will shall be expressed in periodic and genuine elections which shall be by universal and equal suffrage and shall be held by secret vote or by equivalent free voting procedures.
And the International Covenant on Civil and Political Rights, art. 25:
Every citizen shall have the right and the opportunity, without … unreasonable restrictions: (a) To take part in the conduct of public affairs, directly or through freely chosen representatives; (b) To vote and to be elected at genuine periodic elections which shall be by universal and equal suffrage and shall be held by secret ballot, guaranteeing the free expression of the will of the electors.
These are the so-called political rights that together constitute the right to democracy. This right to democracy was once again confirmed by a vote in the UN Commission on Human Rights in Geneva, in 1999 (there were no votes against and only two countries, China and Cuba, abstained).
This is not a novelty. Political rights are as old and as traditional as freedom rights. The French Revolution already claimed sovereignty for la Nation or the people (art. 3 and 6 of the Declaration of 1789).