I am a long-term resident of Japan, and I would be the last person to defend Japanese software in general. I’ve run into particularly horrible user interfaces on government websites and in some internal systems used by my employer.
But a major element behind the success of Japanese convenience stores seems to be the software that manages the inventory, shelf placement, worker shifts, and many other things. The only time I interface with that software directly is when I buy tickets, use ATMs, or print out documents on the multifunction copy machines. Those interfaces work fine. Considering how smoothly the stores operate, the software behind the scenes must be working pretty well, too.