When did you realize nobody truly knows a second language? Its all just illusionary. They trick you with the facade of knowing the language only in a hyper specialized area. Its not like your first language. With your first language, you can talk business, cooking, you could name the planets, casual conversation, shit talk, etc.

With a second language, they may hold a conversation with you, but ask them to name the planets. Ask them to explain how photosynthesis works. Ask them to name legal terms used in court. They dont know it. They dont really know the language. Nobody actually knows a second language. Its mere trickery.