Earlier quoted context omitted.
Isn't Japan the industrialized nation with the lowest fraction of foreigners?
AFAICT, Japan has the easiest immigration for skilled professionals, by far. However, this has been the case for less than 10 years, as they totally revamped their immigration laws in the 2010s sometime to try to attract more such people, so of course it's going to take time to see the difference. Japan is also somewhat difficult for foreigners to live in because of the language barrier, but Germany isn't that differ…
In the case of Japan, you also have the insanely difficult writing system, probably the most difficult writing system in current usage. The German language might be difficult, but at least it uses an alphabet with a somewhat consistent spelling.