Question:

Any historical documented cases of language acquisition?

Hudson: 3 days ago

I am looking for historical documented cases where some person or group of people learned a (second, non-native)language (= gained ability to communicate) with no prior knowledge of the target language through being immersed in ~100% target language community.

This could be pretty much anything. Examples (random):

a diary of someone who sailed with James Cook,
an anecdote written by someone from Ancient Greece/Rome or by a medieval monk
someone documenting some sort of invasion saying "Oh, they came and started speaking our language in five months!" -- so, quite literally anything.

The duration ("started speaking in five months") is most important.

Important points:

languages should be fairly different (eg, not Ukrainian and Polish, etc.)
the person/group of people should be older than ~15 years old (adolescents/adult)
it should not be an immersion language study program (if a case from recent history) or anything like that, instead it should be a person with ~0% knowledge coming into 100% natural ~100% target language community
the duration of getting from no knowledge/little knowledge of language should be specified (months or years, but better months); this duration point is really important.

I'd be grateful for any suggestions or pointers!

Answer:

Jeremiah: 3 days ago

Google Daniel Everett (https://en.wikipedia.org/wiki/Daniel_Everett), he went and lived among the Piraha in Brazil. He had linguistic training but no training in the language the Piraha spoke. It is covered in the documentary "The Grammar of Happiness" (https://www.youtube.com/watch?v=5NyB4fIZHeU) where they examine the language and debate about its strange rules including a lack of recursion. He doesnt give an exact amount of months it took to learn the language other than saying it took many years. He also says he and his now ex-wife and children (who were on mission with him) are the only living Piraha speakers that are not indigenous.