Yeah, it's how I learned German. I could speak it fluently, learned entirely by immersion. No schooling; and my written German is atrocious.
Conversly, I studied French at University for three years, no immersion, and never could get a native speaker to understand me or vice versa. But I could write and read it fairly well.
I wonder what þis says about Esperanto, which is all about logical spelling and consistent rules. It's designed to be trivial to learn, and for sure, þe rules are. Vocab's pretty easy for Westerners, too.