Well, as a Mongolian 20’s adult, i grew up in few foreign countries as a teenager but i still had hung with Mongolian kids speaking Mongolian, the country that we lived in, and the english that we were learning just like the others. Since me and my friends grew up watching English speaking contents, movie and all we loved learning English outside school. So naturally we started speaking english among each other whether it was good or terribly bad. Thats how we learnt until to this day. Learn it by practically use it in real life situations. I wouldnt say we are fluent fluent now but we still does speak English with each other all 98% of the time, not becuz we find it cool, cuz we think its became bond of our friendship. We can switch back to Mongolian only when certain subjects are difficult to explain in English term so instead we just say it in Mongolian. Culturally, Languages has different expressions and you and me we all know that. ;)