LONDON — A British court could give a final decision on Monday on whether WikiLeaks’ founder Julian Assange should be extradited to the United States over the mass leak of secret U.S. documents, the culmination of 13 years of legal battles and detentions.

Two judges at the High Court in London are set to rule on whether the court is satisfied by U.S. assurances that Assange, 52, would not face the death penalty and could rely on the First Amendment right to free speech if he faced a U.S….