Treaty
The end of a treaty, the eschatocol (or closing protocol), is often signaled by a clause like "in witness whereof" or "in faith whereof," the parties have affixed their signatures, followed by the words "DONE at," then the site(s) of the treaty's execution and the date(s) of its execution. The date is typically written in its most formal, longest possible form. For example, the Charter of the United Nations was "DONE at the city of San Francisco the twenty-sixth day of June, one thousand nine hundred and forty-five." If the treaty is executed in multiple copies in different languages, that fact is always noted, and is followed by a stipulation that the versions in different languages are equally authentic.

Q: What is the formal name for the closing protocol of a treaty?
the eschatocol