[kyllo]

Research says our ability to distinguish sounds in other languages ceases after first 8 months and that's why it's harder to understand someone talking in foreign language.

For me this obstacle went away with sufficient immersion and practice. I started learning Chinese at age 19, the following year I went to China as an exchange student and studied Chinese / Mandarin full time. By the time I came back I was fluent in the language, more fluent than all of the second-generation Chinese-Americans I knew, and with a native-sounding accent, although my vocabulary was still not quite native-speaker level.

I don't know exactly what Zuck is doing to study, but what I did was I went to school in China and spoke almost entirely in Mandarin all day, wrote essays in Chinese, read news articles and novels in Chinese, made Chinese friends, dated Chinese women (and eventually married one).

You really have to live in a foreign language for a period of several years in order to truly learn it.