@hazelnot @wfk @quixoticgeek @girlonthenet
just to give a few family anecdotes: my mum speaks Hebrew and English. her dad is a native Hebrew-Yiddish bilingual who also has good English and German. his parents spoke fluently all of the above, as well as Polish.
back then you had to know more than one language, at least a bit, to live your daily life. your community had more than one large linguistic population? then you had to know those two well. you also travelled around, say, as a helper clothes salesman (which was my great grandma's job)? make that three. you migrated several times in your life (as my grandpa did)? make that four.

as a final fun fact, the oldest example of bilingualism i know of is Rabshake's speech in 2 Kings 18, where Rabshake, one of Sennacherib's messengers, delivers a speech to the Judaites telling them they should surrender, delivered in Hebrew. the people of king Hezekiah then ask him to switch to Aramic, because they can understand that language, and by speaking in "Judaite" (i.e. the Judaite dialect of Hebrew) they're afraid he'll scare their people.
https://en.wikipedia.org/wiki/2_Kings_18#Rabshakeh's_speeches_(18:17%E2%80%9337)

@hazelnot @wfk @quixoticgeek @girlonthenet
learning multiple languages in school isn't actually that rare (though it is unfortunately becoming rarer over time). many places around the world have the assumption that an educated person speaks 3 languages.
https://web.archive.org/web/20191215235020/http://www.cal.org/content/download/1803/19986/file/AGlobalPerspectiveonBilingualism.pdf
and multilingualism is definitely not a new phenomenon. on the contrary. people in history often spoke more than one language, it's just that those languages usually tended to be closer to each other, say High and Low German, or Hebrew and Aramic.
https://www.letter-daad.de/en/language/when-multilingualism-is-the-norm/
in fact i'd argue the number of languages a person knows decreased since the days of yore, because of the dominance of English but also due to the concept of "one country one language".
https://www.cambridge.org/core/books/abs/multilingualism-and-education/multilingualism-as-norm/ED39FE06137B49E1C425CC5F1AE8A997