The languages of Russian-Swedish negotiations, congresses, and peace treaties of the reign of Peter I have rarely been mentioned in the works covering the history of Russian-Swedish relations or foreign policy, and they have never become the subject of special research. Based on a vast set of sources deposited in the Russian State Archive of Ancient Acts (RGADA), the Archive of Foreign Policy of the Russian Empire (AVPRI), and the Swedish National Archives (Riksarkivet), the article provides an overview of major diplomatic events of the Russian-Swedish relations of 1718–1724, paying close attention to the language of negotiations, peace treaties, ratifications, and correspondence. At the time, when both sides used their national language, the traditional bilingualism of the Russian-Swedish diplomatic documents coexisted with the active use of the German language as a neutral one. More particularly, this was due to the lack of Swedish translators in Russia and the fact that both Russian and Swedish diplomats were of German descent or spoke German. However, the author argues that the use of German was not obvious and had limits, as languages of diplomacy retained their symbolic meaning. Traditionally, the formation of the Petrine diplomatic system is described as a departure from tradition, the inclusion of Russia into the eighteenth-century state system, and its adaptation to the diplomatic customs of European diplomacy. A review of the Russian-Swedish diplomatic language practices shows that each side employed its language, and Swedish diplomats refused outright to communicate with Russian authorities in German. The author assumes that studying early modern European diplomacy requires a micro-perspective and regional focus. This approach could be more productive for understanding the formation and functioning of early modern diplomacy than the traditional framework of Russian integration into the uniform European diplomatic system.