Immigration isn't going to solve anything, immigration from where ? Japan isn't the US, they aren't talking English nor their society is build in a way it can accept huge immigration waves.
Japan needs to work on techs that will solve its problems, not resort to a massive immigration wave that will only kick the can down the road.
Edit: A lot of people saying "immigration won't work" but not offering alternative solutions.
I hope the insularity ends up being worth it for them, but history is not on their side.
No, this is literally the post-WW2 boom dying off. Occupied Japan underwent a period of extreme population growth in the few decades after WW2 ended. They currently have 125mm people living in a land area the size of California which is 75% uninhabitable (mountains).
Japanese is not an easy language to learn, but its not impossible to learn. If people are allowed in then they will learn Japanese