> is the only known working solution to a decreasing population.

Which it obviously isn't a working solution in any nature of the word. Using arbitrary countries to avoid common mousetraps.

Hypothetically all women in Estonia suddenly opt out of having children for a variety of reasons. They had previously had no problems like this and enjoyed a high fertility rate up until now. The government of Estonia sees this and starts mass immigrating Japanese men and women and are able to stabilize their population. Though, the Japanese women also normalize to the same state of opting out after just one generation.

The government claims that this too is an emergency and seeks another seemingly arbitrary population of humans to import.