nixfiles/configuration/common/locale.nix

{ ... }:

{

  time.timeZone = "Europe/Berlin";

  i18n.defaultLocale = "de_DE.UTF-8";
  i18n.extraLocaleSettings = {
    LC_MESSAGES = "en_US.UTF-8";
  };
  console = {
    keyMap = "de-latin1";
  };

}