How to Fluently Switch From One Language To Another Language

Imagine you're on a train in Belgium. A woman on the train is speaking French on the phone when the ticket conductor comes in. She asks him a question in fluent Flemish. No one bats an eyelid.

Or a guy at a party is chatting to his friends in Spanish, and suddenly an American friend comes in and he enthusiastically greets her in fluent English.

We've all seen it on TV or even in real life, but have you ever wondered how these super-quick switches between languages work?

Alessia, 17 from Ver...