What I want

What I want is to talk with an English-speaking foreigner (better: a foreign who speaks English) and to improve my English. 
I will help them learn Chinese since I can speak it fluently.
I need to learn English because I want to know different cultures from different countries from all over the world. In addition, English is the most popular language in the world.
How can I prove that I am successfully learning English? Well, one day you'll want to talk with me in English and you'll be able to understand me perfectly.

Good job! Keep on writing and reading. Feel free to ask any questions about a correction you don't understand.

what i want

what i want is to talk with foreigners who speak English thus improving my oral English,
i will help him or her to learn Chinese since(untill ?) i can express my opinion fluently .
why i need to learn english is that i want to know different cultures of different countries all over the world, another reason is that English is the most popular language in the world .
how i can prove i am successfully learning english ?obviously,one day you want to talk with me in chinese and what i explained to you is really easy to understand .(这句真的是没明白想表达什么)