A relict of the 18th c. position of France as a world power and French as the lingua franca of European royalty and diplomats, many French words dealing with government and diplomacy were either taken over directly into English:
attaché, chargé d’affaire, communiqué, détente, rapprochement
or adapted, preserving postpositive adjective word order:
secretary general, ambassador extraordinary, ambassador plenipotentiary
USAmerican passports still contain French translations of some text, with Spanish appearing during the second Clinton administration as a nod to Puerto Rico, whose residents are American citizens but without the right to vote on the island, though they may do so if they become permanent residents of one of the 50 states.
The Directorates-General of the European Union, headed by directors-general — both with hyphen — follow this naming convention.