Let me throw my 2 cents in here.
Rights, by definition, can be either legal, social, or ethical.
Beginning with the ethical - you can claim that ethics are subjective, and that's true to a marginal extent, but, largely, human ethics are universal. Nearly every culture on earth has an ethical system that boils down to the golden rule: do to others what you would have them do to you. In other words, treat people as you feel you deserve to be treated. That forms the foundation for what we might call "natural rights."
Socially, if we can agree on this guiding ethical principle, we then interpret this and begin to structure society in a way that protects these rights for the members of that society.
We then come up with laws. Laws which, of course, are unique to specific goverrmsnts and cultures but which, nonetheless, share a number of guiding principles.
For instance, murder is illegal in nearly every culture on earth. This implies a right to life. Theft and slavery are nearly universally illegal. This implies the right to property and liberty.
You see, we get so hung up on our differences sometimes, we start to believe morality and legality to be completely subjective and cultural. In fact, our commonalities are much more profound and run much deeper than our differences.
Every child learns not to hit other children, to share, to treat others with respect, etc. These shared values carry in to adulthood and in to the laws which we create for ourselves.