I have a friend who seems to pick up languages by osmosis. We went for a meal and were served by someone from Croatia. My friend started chatting to him (in English) and asked him for a few words in Croatian (no more than about a dozen) then was able to start speaking to him in Croatian. Afterwards he explained the few words let him know some basic structure he could relate to other languages he knew and he could extrapolate from them and the new words enough to be able to have a conversation. It was both spooky and amazing at the same time. He has a library in dozens of languages and gets books 'just to see what the language is like' - it's like some sort of super-power.