I just read up on it and, if I’m understanding it correctly, it wasn’t intended to be ratified by individual countries. It was intended as a policy statement by the United Nations Educational, Scientific and Cultural Organization.
Cite (I added the underlining to the relevant part.)
The United States was a member of UNESCO in 2005, when this declaration was ratified. So I assume we were among the countries which “unanimously ratified” it.
However, we withdrew from UNESCO in 2018 so I don’t know what our current status is in regards to the policy.