Germans aren't having children. Germans spend their treasure on holidays, nice restaurants, and extending their adolescents into middle age.
German baby boomers are now moving past the age where they even can have children. ‘Germans’ of the future will be people who immigrated there and chose to have families rather than indulge themselves in shallowness... I don't believe the situation can be turned around...
If there is no God ( and most Germans are liberals who are waaaaaay to sophisticated to believe in conservative ideas like religion) then why not base your life on 'what feels good'? Of course if your life is based on 'if it feels good, do it', why sacrifice for children? Children take work, commitment and a belief in the future. A belief beyond 'what feels good'.
So the Germans are going to die out. Same with the French. Their languages will die with them... Happens. No one speaks Latin, right?
Quite some hyperbole in your post. OK, Germans *are* having children, albeit at a rate below replacement/growth. So the population will shrink, probably for a some years, even decades.
BUT, the children that *are* born are not sterile. There is nothing that will prevent *them* from having larger families than the current generation.
It may go against the agenda of cultural pessimism, but I can see things swing the other way again.
100 years ago German families typically had 3, 4, 5, or more children. The children born today by the baby boomer parents often have no siblings.
Imagine these children thinking, "hey, it would've been nice to have some brothers and sisters when I grew up. *I* will have a large family like my great-grandparents had." And when that happens, the current trend is stopped and turned around.
There is ample empiric data that shows that younger generations do things different than the generations of their parents and grandparents. Swings between a conservative and liberal mindset etc. Why not have a slightly more optimistic outlook?