add TODO

src/Umbraco.Web.UI.Client/src/shared/lit-element/lit-element.element.ts

@@ -1,6 +1,8 @@
 import { LitElement, property } from '@umbraco-cms/backoffice/external/lit';
 import { UmbElementMixin } from '@umbraco-cms/backoffice/element-api';
 
+// TODO: Currently we don't check if the `lang` is registered in the backoffice. We should do that. We can do that by checking if the `lang` is in the `languages` array of the `language` resource and potentially make sure that UmbTranslationRegistry only loads the translations and some other mechanism reloads to another language (currently it does both)
+
 /**
  * The base class for all Umbraco LitElement elements.
  *