Hi,
The behavior was by design and we have no idea why it changed, but you may feedback such findings in below user voice forum:
General Feedback-Windows Server
https://windowsserver.uservoice.com/forums/295047-general-feedback
Per further checking, Server 2012 provided 2 options for Dutch:Belgium and Netherlands (less than server 2019), while for the latter option, the digital grouping symbol is dot. And in Server 2019, the default symbol for Dutch(Netherlands) is the same.
Hope this helps and please help to accept as Answer if the response is useful.
Thanks,
Jenny