I want to make friends with some foreigners, so I want to learn English.I also want to improve my English grade.

Above is a corrected form of your sentence as you formed it. This structure is acceptable, but I suggest the following, which is a bit more natural:

I want to learn English so that I can make friends with foreigners. I also want to improve my English grade.

Alternatively, you could just replace the second "want" with "need".

Overall though, great work! You are well on your way!