How during any period really before knowledge was freely around from person to person, before books were common occurrences and many people were illiterate how would one go about learning a different language? in most aspects of life it would be useless to learn a second language if you were a farmer but let’s say youre king of england during the early 10th century and you go to speak to the king of france about a peace negotiations but you don’t speak french, how would a noble go about learning said language? and would they even attempt to do so? would they have translators or the dark age equivalent as such or would there be kings dedicating time to another language from a foreign land?
Honestly, speaking as a language learner, plain study is insufficient. Indeed, it baffles me that anyone learning a language does so by studying it. That might give you a grasp of rules and vocabulary, but it really needs to be combined with actual use. (I will forever be an advocate of using survival pressure to drive language acquisition - that is, the "learn or die" method.) This is not yet getting into cases where people might have to grow up knowing multiple languages (hi). More can always be said on language acquisition, so if anyone would like to make their own reply, please don't hesitate to do so! For the meantime, here are some previous posts that cover this matter.
u/WelfOnAShelf has a collection of their answers regarding language acquisition, those being these three threads:
Saving me the trouble, u/myfriendscallmethor also has a language acquisition compilation.