Have you seen this movie? It’s the one where Bill Murray is stuck repeating the same day over and over (which happens to be the American ‘Groundhog Day’). Every interaction begins the exact same way. “Good morning, Bill. How’s the weather?” Or whatever. The repetition becomes so certain that Bill begins to experiment; in one case, he punches a guy in the face!
Imagine you were stuck in Groundhog Day in a foreign country. In a week you could become fluent in the language—fluent as far as anyone would know. You’d simply learn the exact words and phrases needed to satisfy the predictable interactions of that day, and you’d be done.
The secret is that linguistically, everyday is Groundhog Day. The relatively few words and phrases you’ll need on a given day, are the same you’ll need everyday. The grammatical patterns of the language will be the same, and even the content of conversation—greeting, weather, work, etc.—will be relatively unchanging.
Your goal in learning a language is to exploit the repetitious nature of life and language to create a Groundhog Day situation for yourself language-wise.