i have skied in japan for the last 3 seasons before this year, twice at niseko and once at furano. i do speak some japanese so maybe im not totally up on how a non-japanese speaker would find it, but in any case here's my take on the 2 resorts
I think Niseko is a fantastic resort. There are plenty of runs for an intermediate skier and definitely some more advanced runs as well if your friend improves. There is little in the way of "expert" terrain but given your friend is an intermediate i dont think that would bother them. There is more than enough variety to keep yourself entertained for 10 days or more, and night skiing there is fantastic (every night they light up most of the mountain until 9pm). Snow quality of course is amazing, and it just never stops snowing there
On the negative side, it has been totally overrun by aussies, and I dont think you will find much in the way of japanese culture there anymore. Although everyone in Niseko speaks *some* english now, don't go there for a japanese experience. Its still a japanese village, but doesnt really feel so japanese.
to get there its about 2 hours from sapporo airport and any package deal company will take care of it for you, very little hassle involved.
Definitely an intermediates mountain. If you love wide open groomers then furano is the place for you. There are tons of long, wide runs that are really really good for someone of beginner to intermediate ability, but very little beyond that. There is only 1 real black run (kumatoshi if i remember correctly) and ski patrol only open it twice a day for 10 mins at a time. If your friend is at a lower intermediate level i would recommend furano, anything beyond that probably not.
most of the hotels are on the mountain, but furano itself is an actual town about 10 mins away by bus. furano town is totally japanese and hasn't yet been overrun by westerners. people in the town probably wont speak much english. so it is definitely much more of a japanese experience than niseko.
furano is about 3-4 hours from sapporo airport by bus and again it is very low hassle, any package tour will take care of it for you
hope this helps and feel free to post any questions