trui wrote:For people who are interested in learning lots of languages though, I could see being more picky about what words one learns as beneficial.
I don't think that is being discussed here. Learning several languages doesn't mean being picky as if we had only a limited amount of word slots in the brain and had to divide them among the languages. There are exceptional people, like the guy who learnt a French dictionary to win a scrabble tournament, who show us we are far from reaching our total capacity. Sure, it doesn't mean that every human being can do that, just like not everyone can run like Usain Bolt. But it is safe to believe we can learn much more than we think.
It is rather the opposite, we are improving the vocabulary, even when learning several languages, and the question is how many words are enough for each learner.
I find it interesting that some numbers get repeated on the vocabulary books' covers, titles of memrise decks, and so on. The numbers I can remember seeing are :
1000 (ok, we'll probably agree this is not a serious "final" goal, it is just an easy set of data app creators can give a new cover to enjoy the profit),
2000 or 3000 (serious traditional courses),
4000 (various vocabulary books, supposedly the vocab for GoetheB1),
5000 (a nice number perhaps, various memrise courses are a good example),
10000, 13000, 15000, and 20000 are still in my library as vocab books "to be learnt".
Jumping a bit higher, 35000 is already a middle sized monolingual dictionary, therefore originally not meant to be memorized. But the awesome +French courses on memrise by Eunoia make up to approximately 35000 words too.
Looking at some random rarer words on the +French lists (based on the Lexique database), I think 35000 is not an unreasonable passive goal for anyone regularily reading in the language. Especially considering the overlap between various european languages. The deeper in the frequency you get, the further you get towards interesting not everyday stuff, the more overlap you find. Even in not obviously close languages like Czech and French, and of course not all these words are totally original, a noun and the verb from the same root are counted separately, and so on. As active vocabulary, 35000 is quite a challenge, but potentially very rewarding as that might be quite close to usual natives. The authors of resources my little number list comes from seem to suggest that something like 15000 is already absolutely awesome for a learner, and something like 4000 is B1, therefore covering most everyday situations and conversation topics.