nix-config/home/xdg-user-dirs.nix

{
  xdg.userDirs = {
    enable = true;

    desktop = null;
    templates = null;
    publicShare = null;

    download = "/home/user/ダウンロード";
    documents = "/home/user/ドキュメント";
    music = "/home/user/音楽";
    pictures = "/home/user/画像";
    videos = "/home/user/ビデオ";
  };

  xdg.configFile."user-dirs.locale".text = "ja_JP";
}