nixos/config/locale.nix

{ config, pkgs, ... }:

{
  console.keyMap = "de";
  i18n = {
    defaultLocale = "en_US.UTF-8";

    inputMethod = {
      enabled = if config.services.xserver.enable then "fcitx5" else null;
      fcitx5.addons = with pkgs; [ fcitx5-chinese-addons fcitx5-mozc fcitx5-table-extra ];
    };
  };
}