I've already asked operagust to define "decent". I don't see the point in providing your own POV on that, ishibai. I hope you aren't trying to steer the conversation away from what operagust wants to learn by doing that.
In Japan I would say a decent lifestyle would encompass having a car
I disagree, and your reason makes no sense at all.
being able to eat safe healthy good quality food,
I also disagree here, mainly because I don't think this enters into the word "decent", but rather mere common sense.
go out at the weekends for entertainment,
Again, disagree, assuming "go out" means go bar hopping.
partake in a sport,
I hate most, so here again I have a contrary opinion yet still lead a decent life in my own definition.
furnish your safe, well built accommodation with quality aesthetic and comfortable furniture
Loaded point which I'll ignore for a couple of reasons, one being "common sense" enters here again.
and be able to travel a few times a year.
Depends where, domestically or abroad, and how long, and that is an individual choice.
You would need to make 300.000 plus housing, be single and not want to save for this to be possible.
"not want to save" (?) begs the question of anyone's idea of a decent living. Besides, depending on whether one lives in a large, medium, or small city, 300K just barely gets one by, especially with a car.
operagust, please answer soon!