Not quite as simple as 1 spot.
For powder Hokkaido (Niseko being the most popular resort).
In general the terrain tends to be a little less steep and the mountains smaller than Honshu, the main island.
Still some amazing terrain to be had though.
For steeper terrain and bigger mountains there are a number of places in honshu that are very popular.
Nagano, Niigata, Yamagata (Zao) and in Aomori (Hakkoda) .
Nagano tends to be the most popular (Hakuba).
They all get hit by great powder, but Hokkaido has the best and the most powder, no doubt.
As for Japanese language as I said its a huge bonus if you can speak some, but not essential.
I have been here with 0 Japanese and got by OK.
I now speak, read and write fluently and do professional translation work.
It makes things much more fun and opens more options up but its not essential IMO.