I can share some general anecdotes about language misunderstandings and surprising moments that have occurred between people who didn't think someone else understood their language.
A multilingual traveler's surprise: A person was traveling abroad and spoke their native language, assuming the locals around them couldn't understand it. However, to their astonishment, they later discovered that many people in that foreign country were bilingual and understood everything they were saying.
Secret conversations: In some workplaces, coworkers might speak in their native language to discuss private matters, assuming no one else understands. On occasion, someone may unexpectedly reveal that they actually comprehend the language, leading to amusing or awkward situations.
Sensitive remarks: People sometimes make unkind or judgmental comments about others in a language they believe no one else understands. However, in multicultural environments, there's a chance that someone present understands the language and can feel hurt by these comments.
Negotiating advantages: In business or negotiation settings, one party might secretly understand the other party's language, giving them an unexpected advantage by knowing what the other side is planning or discussing.
Language learning surprises: Foreign language learners often experience moments of joy when they understand native speakers talking about them or complimenting their language skills without realizing they understand.
It's important to be cautious about assuming language barriers and treating conversations with respect, even when you think no one else can understand what is being said. Misunderstandings and surprises can occur in various social settings, but it's always best to communicate openly and kindly to avoid unintentional consequences.