Intoroducing myself

Hello there!
I'm a high school student and I majored in an international course at school. (this is happening now or in the past?)
I'm interested in foreign countries and cultures.
I especially like Britain, Sweden and Norway. So far, I've been to Norway and Sweden.

I want to improve my fluency in English (this is more colloquial) and make friends :-)

If you like, I can teach you Japanese.

Intoroducing myself

Hello there!
I'm a high school student. I majoring in an(depend on how many courses you are in) international course at school.
I'm interested in foreign countries and cultures. (multiple amount of cultures)
I especially like Britain, Sweden and Norway. Also, I've been to Norway and Sweden.
I want to increase my English ability and make friends :-)
If you want, I can teach you Japanese.

Very good :D just need to improve in the grammars such as plural, past and present tense. 

I'm majoring in International Relations. (or Law, Buisness, etc) 

if you have not finished yet

I'm interested in foreign countrys and cultures.

if you're interested in more than one 

I want to improve my English and make friends :-) 

"improve" for better quality, "increase" for greater quantity 

All of above are just suggestions :)