I learned English as a kid by trying to read the manual for game maker. I'd sometimes get my parents to translate little bits, but they had better shit to do than sit there and translate line by line.
Somehow I managed to bootstrap that into (IMHO) pretty fluent English. Ask me to do something similar today and I am 100% sure it'd be impossible.
Though as a kid I do remember playing RPG games in a language I don't know at all.