Complex sentence: In 1778, he was appointed Minister Plenipotentiary to the Elector of Trier until 1783, when he was posted as a Special Envoy to London following the peace treaty signed between Britain and France.
Split into simpler sentences: In 1778, he was appointed Minister Plenipotentiary to the Elector of Trier. In 1783, he was posted as a Special Envoy to London following the peace treaty signed between England and France.