The subject of the article is the concept of a universal language and a reflection on its importance for law. The starting point is a presentation of the history of the concept of a common language for all mankind, a concept that has always accompanied man – it is present in the Bible, in the ancient writings of Near Eastern peoples, it was alive in the Middle Ages and during the Renaissance, and it experienced its particular heyday – among other reasons because of the gradual abandonment of Latin as the language of science – in the seventeenth century, an age that was reformist by definition. Since its inception, the concept of a universal language has been inextricably linked with the idea of world peace and universal happiness for all people. It is significant that in most universal language designs, regardless of the era, there were, to a greater or lesser extent, references to the utility of such languages for law. The author, tracing the development of the concept of a universal language, focuses on its fullest contemporary development: Esperanto. Esperanto, like previous universal language designs, places particular emphasis on ideas linked to the concept of a universal language, especially the idea of peaceful coexistence and understanding between peoples. In this context, it is reasonable to ask what role Esperanto can play in the development of certain branches of law, especially international law. Given the position of English as the language of legal acts of international importance, the answer to this question is currently not clear.