D:\>type test-locale-stl.cpp
#include <iostream>
#include <clocale>

char *
query_locale_name()
{
  return std::setlocale(LC_ALL, nullptr);
}

int main()
{
  std::setlocale(LC_ALL, "norwegian-bokmal.UTF-8");

  std::cout << "locale before: " << query_locale_name() << std::endl;
  std::cout << 0.1 << std::endl;
  std::cout << "locale after: " << query_locale_name() << std::endl;
}

D:\>cl /EHsc /W4 /WX /std:c++latest .\test-locale-stl.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.44.35217 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

/std:c++latest is provided as a preview of language features from the latest C++
working draft, and we're eager to hear about bugs and suggestions for improvements.
However, note that these features are provided as-is without support, and subject
to changes or removal as the working draft evolves. See
https://go.microsoft.com/fwlink/?linkid=2045807 for details.

test-locale-stl.cpp
Microsoft (R) Incremental Linker Version 14.44.35217.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test-locale-stl.exe
test-locale-stl.obj

D:\>test-locale-stl
locale before: Norwegian Bokmål_Norway.utf8
0.1
locale after: C