I'm a fairly open borders guy, but if you want to have near-zero immigration to avoid foreigners, the country HAS to improve the life of persons, particularly women, so that having children and raising them to adulthood is a activity that is more joy than stress. Otherwise, you'll go the way of South Korea.
Of course, the "correct" behavior is to not treat foreigners as other, but as "merely" different aspects of self. Then seek to integrate all tolerant persons that want to immigrate; likely through multiculturalism.
I'm all for persons voluntarily opting to have fewer (or no) progeny. Certainly, that is my intent.
But, Malthus was wrong on so many levels, and regulating reproductive activity even with the best of intent is going to be abused by eugenicists for genocide.
The already posted SK vid explains how the current social systems in most countries need at least replacement birth rates. It might be possible to have a society that could survive less-than-replacement birth rates, but I don't see how.