People have the misconception that learning more languages will allow you to make more friends.  I've found it to be the opposite really.  When you start really digging into a language, usually about after 2 years of really studying it hard, you'll get to the point where you surpass a lot of uneducated native speakers in their own language.  You might have an accent, but your vocabulary and mechanics will be superior to theirs.

When this happens they're not going to like you for it.  It will be seen as you robbing them of something.  This is especially true if you're crossing racial lines.  Happens to me all the time.

Language learning is a very lonely road.  As you get better, it's harder to find good materials, you make less friends, and you create more enemies.  So you gain knowledge, but you do pay a price for that knowledge.

Culture really means very little these days with the internet.  "Culture" is sort of optional in most developed countries, so that means by definition that it's non-existent.  

Depends what people mean by "friends", but, saying that, it is easier to have a conversation with somebody you feel comfortable with.

The main reason is probably that they feel along. They then use learning another language as a way to make friends. It also brings the perks of another culture and friends you can someday meet in person if you go to visit their country.

i think that many people are alone and try to find freind in Internet  

I wanna know their culture and may be their language . who knows may be on day i travel there and couple of friends can help so much.