A person’s accent is not rigid – it changes a lot throughout your lifetime. It’s not just your vocabulary that expands the older and wiser you get. The way you pronounce words, your stress pattern and even your intonation can change drastically. It all depends on what you experience, where you spend most of your time, and who you talk to. That change is most apparent in people who moved away and now live in another country than the one they grew up in. As silly as it sounds at first – this means you can lose your native accent.
It’s good to see that some actors are aware of the flexibility of their accent and decide to work with a dialect coach to regain their native accent – like Gary Oldman did when he had to do an English accent after having lived in the States for a long time. Like Gary Oldman says in the interview above, a speaker might not even notice that some foreign features slipped their way into their speech. Sometimes tiny nuances can make or break an accent and a dialect coach can point out those small features that the actors themselves aren’t aware of.