This broke as a side-effect of https://github.com/electron/electron/pull/19159, so it's broken starting in the April 2 nightly of 14.0.0 up to now.

Current behavior is that, instead of dialog buttons having text such as `Open` or `Close`, they read `gtk-open` or `gtk-close`.
shell/browser/ui/gtk_util.cc
static base::NoDestructor<std::string> gettext_package(
      "gtk" + base::NumberToString(gtk::GtkVersion().components()[0]) + "0");
  return gettext_package->c_str();
}
const char* GtkGettext(const char* str) {
  return g_dgettext(GettextPackage(), str);
}
const char* GetCancelLabel() {
  if (!gtk::GtkCheckVersion(4))
    return "gtk-cancel";  
  static const char* cancel = GtkGettext("_Cancel");
  return cancel;
}
const char* GetOpenLabel() {
  if (!gtk::GtkCheckVersion(4))
    return "gtk-open";  
  static const char* open = GtkGettext("_Open");
  return open;
}
const char* GetSaveLabel() {