[enyafriend]

As a rule of the thumb, one who has attained the Japanese Level 1 would know enough most basic vocabulary and would be good enough to hold a basic conversation, though, with errors here and there.

Of course, as one's JLPT Level improves, their language proficiency and understanding would gradually improves.

But then again, conversational Japanese proficiency requires constant practice. A high JLPT level does not neccessarily translate to a high level conversational fluency. Only constant practice does that.