-1! Sometimes it works but there is a certain amount of vocabulary that an average person cannot pick up, just immersing in a culture does not necessarily work.
There's only that much vocabulary that one needs in order to manage. You can rest assured that medical vocabulary isn't part of it, and that many native speakers might not necessarily be familiar. It's OK.
I know that some people have more of a knack for languages than others, but few will find methods other than immersion (speaking and reading) better (many non-English speakers pick up English by watching English speaking TV with subtitles in their native language, but that doesn't work for everyone).
I remember when I was in Yeshiva there was an older Israeli bochur who wanted to learn English. He would borrow English books with stories of Tzaddikim for children, try to read as much as he could on his own, and then came to me for whatever he couldn't figure out or for review.
At a very young age I raised bilingual at home. My third language was acquired by immersion (also at a young age). I picked up Aramaic (non-conversational) through learning Gemorah and saying שניים מקרא ואחד תרגום. Is my Aramaic vocabulary complete? Absolutely not, but in most cases I can pick up an unfamiliar Gemorah, or read one of the more elaborative תרגומים and comprehend what I am reading, even if I am unfamiliar with 5% of the words or expressions without looking them up. One of the languages I spoke as a toddler is somewhat forgotten (since my grandmother passed away I had no use for it, though it would have come handy starting in my teenage years, and I can still understand some) and another language was picked up in my late teens and is one of my primary languages to this day.
So to summarize, I can tell you from personal experience: 1. There's nothing like immersion for learning a language. 2. You don't need to have a complete vocabulary of more than several hundred words in order to manage.
ETA: My son is somewhat of an autodidact, and decided at some point to learn Esperanto as a gateway to learning additional languages (he already knows a few). Since immersion isn't really possible (or practical) in Esperanto, he was practicing using Duolingo.
