Though speakers and listeners monitor communication success, they systematically overestimate it. We report an extreme illusion of understanding that exists even without shared language. Native Mandarin Chinese speakers overestimated how well native English-speaking Americans understood what they said in Chinese, even when they were informed that the listeners knew no Chinese. These listeners also believed they understood the intentions of the Chinese speakers much more than they actually did. This extreme illusion impacts theories of speech monitoring and may be consequential in real-life, where miscommunication is costly.