I'm not sure those people are hyperpolyglot (whatever that exactly means). They usually have extreme skills in two languages, one being their native language.

I'm not sure those people are hyperpolyglot (whatever that exactly means). They usually have extreme skills in two languages, one being their native language. However, a task like simultaneous translation is tough. It requires a different way of focusing, and has other demands on working memory. There is some evidence that it leads to "functional" changes in the brain. That could be a factor. OTOH, since the effect is bound to a small group living in a few places, it could just as well be a life-style effect.