The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License. Creative Commons License

// raw code

#include <iostream>
#include <locale>
#include <format>

// define facet for German bool names:
class GermanBoolNames : public std::numpunct_byname<char> {
  GermanBoolNames (const std::string& name)
   : std::numpunct_byname<char>(name) {
  virtual std::string do_truename() const {
    return "wahr";
  virtual std::string do_falsename() const {
    return "falsch";

int main()
  // create locale with German bool names:
  std::locale locBool{std::cin.getloc(),
                      new GermanBoolNames{""}};
  // use locale to print Boolean values:
  std::cout << std::format(locBool, "{0} {0:L}\n", false);  // false falsch