sorry you cannot
Dammit!
aww what
What the matter?
how do you know?
not even those guys with eidetic memory, perfect pitch and awesome mental “association powers”?
what about people with time (no job, family, or any other hobby -I mean 4 really free weeks not just a couple of hours every other day), mobility, motivation/need, discipline, previous knowledge/experience learning languages, language family ties (for instance from spanish to portuguese, from italian to french, from english to afrikaans and so on), techniques…, and…, and…, and…?
and, my favourite one: what do you really mean with fluency??? I’m really “fluent” in some fields of my own native language and just a mime in others
but yeah, mere mortals (like most of us) would tend to need more than four weeks to get “the gist of a language” (3 months, 6 months, 1 year, 3 years, 5 years, 7 years, 9 years, …)
*the gist of a language = pretty decent foundations