The problem is "conversational" means anything from "hello", "how are you", "my name is", "the horse is on the window" [%] to an actual conversation that can convey something useful.

Between a reasonable degree of grammar correctness, some vocabulary, and the pronunciation needed to make yourself understood it takes some time to carry out any conversation beyond tourist level.

Given that I have plenty of polish friends and contact with the language the "few weeks" is either an exaggeration or, more likely, the bar for "close to conversational" is set relatively low and differs from other people's definition leading to this discussion. Unless it's someone who already speaks a language that's "close enough", maybe czech?

[%] Actual example used by my french teacher a few decades ago.