You are correct. I was misunderstanding the issue. Thank you for helping me understand this.
The calendar supports a left to right and a right to left layout. Each language can specify which direction the calendar should display in. This is what causes the calendar to show up properly in languages like Hebrew.
There was a bug in the calendar that caused it to not interpret this property correctly. The result was that it showed Japanese in right to left mode.
I have just fixed this problem and released that fix in version 3.6.7. That should resolve this issue and make the days display in the correct direction for Japanese.
I’m sorry it took so long to fix this issue. I was unable to understand it since I am not fluent in Japanese.
Thank you for your help.