nixos-configuration/modules/i18n.nix

{...}: {
  config = {
    time.timeZone = "Europe/Berlin";
    i18n = {
      defaultLocale = "en_US.UTF-8";
      extraLocaleSettings = {
        LC_ADDRESS = "de_DE.UTF-8";
        LC_IDENTIFICATION = "de_DE.UTF-8";
        LC_MEASUREMENT = "de_DE.UTF-8";
        LC_MONETARY = "de_DE.UTF-8";
        LC_NAME = "de_DE.UTF-8";
        LC_NUMERIC = "de_DE.UTF-8";
        LC_PAPER = "de_DE.UTF-8";
        LC_TELEPHONE = "de_DE.UTF-8";
        LC_TIME = "de_DE.UTF-8";
      };
    };

    services.xserver = {
      # Configure keymap in X11
      layout = "de";
      xkbVariant = "";
    };

    # Configure console keymap
    console.keyMap = "de";
  };
}