This paper takes as its subject a set of dictionaries published in Russia between 1787 and 1791 called the Comparative Dictionaries of All Languages and Dialects (Sravnitel’nye slovari vsekh iazykov i narechii, known to Western readers as Vocabularia comparativa Linguarum totius Orbis). This hugely ambitious endeavor was commissioned by Catherine the Great and aimed to provide definitions of 285 terms in up to 279 languages of Europe, Asia, Africa, and the Americas. The data contained in these dictionaries offers an effective snapshot of the nascent functions and values of foreign languages in Russian society at the turn of the nineteenth century. Among these, Japanese in particular emerges as a focus of interest: Japanese is the only language represented in a special appendix to the Comparative Dictionaries that contains an update. This was provided in 1791 by the castaway merchant Daikokuya Kōdayū and sought to remedy the preexisting data, which had suffered from numerous methodological pitfalls and a lack of accuracy. This paper considers the two sets of Japanese data contained in the Comparative Dictionaries and contextualizes them in the history of the Japanese language in Russia as well as Russo-Japanese relations. As I argue, this rare lexicographical material, offered twice in the span of just five years, serves as a material-historical tool that reflects the growing mutual awareness between Japan and Russia and constitutes a milestone in the developing political and cultural relationship between the two nations that would come to a head one hundred years later.