Why we learn English as the most important foreign language? why we have to?

This afternoon,when Jason was giving his speech
Alex kept asking the reason why we Chinese should learn English.
yeah..why?
why does the government choose to make English the foreign language of instruction?
we learn English to communicate with the world,but we seldom talk to others in English,though we may know more grammar than Alex
but actually get little.
without talking,will those vedios or magazines work？
why there are still many mistakes in our speeches or writings although we ve been learning English since we are in primary school？
why？