“Most long-term migrants know what it’s like to be a slightly rusty native speaker. The process seems obvious: the longer you are away, the more your language suffers. But it’s not quite so straightforward. In fact, the science of why, when and how we lose our own language is complex and often counter-intuitive. It turns out that how long you’ve been away doesn’t always matter. Socialising with other native speakers abroad can worsen your own native skills. And emotional factors like trauma can be the biggest factor of all.”