Can Italians Understand Spanish? Language Closeness Exacerbates the Illusion of Understanding

People often understand parts of languages that are closely related to their native tongue. But do they understand what the speaker intends to convey? We discovered that linguistic similarity induces an illusion of understanding, leading people to believe they understand more than they actually do. In Study 1, adult native Italian speakers overestimated their understanding of a speaker's intent more when they listened to Spanish (close language) than to Northern Jiangsu Chinese (distant language). In Study 2, adult native Mandarin Chinese speakers overestimated their understanding more when they listened to Northern Jiangsu Chinese (close language) than to Spanish (distant language). When listening to the closer language, listeners were more confident, and this mediated their overestimation of understanding. An illusion of understanding, then, increases not despite language closeness but because of it. This has theoretical implications for the role of calibration in communication and practical implications for miscommunication in international settings.