I use English as my main language and as such am extremely proficient in it, though my proficiency in literature is horrendous. Although I do understand Chinese to a certain extent, I have absolutely no knowledge on Chinese history, culture, beliefs, tradition, pop culture, dialects, or politics. In fact, the only thing I know about Chinese is the language. And even that's not perfect.
I used to attend Japanese lessons as a Ministry Of Education-sponsored third language programme but left the program due to a lack of time available to study for both it and schoolwork. I'm actively learning Hebrew in my leisure time and so far have mastered (and memorised) the entire song Hatikvah, can type most words in Hebrew accurately and quickly, and am now learning basic sentence structures and nouns.