Restore language selector but make it inert

Closes #3529159

project_template/web/profiles/drupal_cms_installer/theme/css/installer-styles.css

@@ -245,3 +245,9 @@ body.install-page {
     height: 100%;
   }
 }
+
+.cms-installer__language-switcher {
+  position: absolute;
+  right: 0;
+  top: 0;
+}