@Jaqen,
Jaqen wrote: he claims that he speaks American East Coast English since he lived there for 30-odd years.
The reality is that some people never become good at using a foreign language.
I know that people think native language usage can be taught, but I believe it's like musicality - you either have it or you don't. People can practice and get better, but some people never truly pick up the cadence of other languages.