As far as I know those who have gone to Japan for the post graduate they have gone through the links. Now none of them are there already returned to Nepal. I am sorry I don't have much idea on it. And most of them who have gone there do the PhD. If you want to know more just surf the net search medical university and get the idea.
For UK, if you want to do MD there is no such degree. First you will have to do MRCP or MRCS (Now these degree has been considered to be recognized as diploma in Indian, Nepal etc.), then you will have to go for FRCP or FRCS according to your speciality. Both of these are very painful.
MRCP:
MRCS
There are member/user from UK hope they will give you more idea about it. And don't forget to visit.
PLAB, MRCP, MRCS [
http://www.xenomed.com/forums/plab-mrcp-mrcs ] section in the xenoMED. If you are considering to go for MRCP/S you will have to pass IELTS with 7.0 and then PLAB. None of this exams are easy and not impossible either.
And let me tell you, NHS (National Health Service), UK opt for the european union graduate then us. Rules and regulation are being made which will create problem for international medical graduate.
Yes
USMLE [
http://www.xenomed.com/forums/usmle ] is for USA.
Best of Luck.