> The biggest thing I've felt since moving here: whether or not you can speak and interact in Japanese makes a world of difference. Seriously.

Literally right for almost every country: France without knowing French, US without English, Taiwan with Chinese or Taiwanese, Egypt without Arabic... Japan is not special in that regard, save for the fact that most people here have quite a low level of English (which is also not very specific to Japan).

So I wholly agree that making the effort to learn the local language repays by itself for any medium or long stay.