Yes the population decline is alarming but does slowing growth really matter when you have a strong culture?
I don’t believe the solution to their problem is importing random people who share nothing in common with their culture.
The Japanese should be able to maintain their culture and I am sure they will bounce back. They owe it to nobody to radically change their culture to appease some number crunchers.
And I say this as an immigrant to US. I’ve been to Japan and it’s just quite amazing.