As someone who has been living in Vienna for the past 4 years (and whose German is his 3rd language), I can tell you that that was certainly not my experience- I could speak basic German at 6 months but it took much longer than that to become fluent.

On the other hand, I've heard from friends who spent some time in South America that Spanish is an exceptionally easy language to learn, and that they could speak half-way fluently within several months.

To bring in the other extreme, I know people who lived in Japan for years and have only learned fairly rudimentary Japanese.

It is very dependent on the person and the language.