English as the world’s lingua franca isn’t going anywhere. Why, then, should we Anglophones bother to learn another language? What’s in it for us? And what, more seriously, are the implications if we decide not to bother?

Digging deeply into these questions, Marek Kohn’s book asks what it actually means to have some mastery of another language (is that the same as being ‘fluent’, or being able to ‘speak’ another language?), and looks at language acquisition, at how the language we happen to speak can alter perception, whether there are cognitive benefits to multiple language use, and what roles the state...