I found lots of examples of both in dictionaries but cannot see any regularity.
Usually choice of an article depends on whether I mean a specific object or a class of objects.
But what exactly is meant when it comes to "right"? Is it ability to do something or a specific case when I do it?
For example, in the sentence:
I have _____ right to vote, because I'm 18.
what should I use?
There is the cite on https://en.wikipedia.org/wiki/Rights from Stanford Encyclopedia of Philosophy:
A right to life, a right to choose; a right to vote, to work, to strike; a right to one phone call, to dissolve parliament, to operate a forklift, to asylum, to equal treatment before the law, to feel proud of what one has done; a right to exist, to sentence an offender to death, to launch a nuclear first strike, to carry a concealed weapon, to a distinct genetic identity; a right to believe one's own eyes, to pronounce the couple husband and wife, to be left alone, to go to hell in one's own way.
All these "rights" are used with "a".
The first result of the search of "right examples" in Google reads:
Some examples of human rights include:
The right to life.
The right to liberty and freedom.
The right to the pursuit of happiness.
The right to live your life free of discrimination.
The right to control what happens to your own body and to make medical decisions for yourself.
How can that be explained?