Add dbp-lang event

packages/app-shell/README.md

@@ -36,6 +36,13 @@ The component emits `dbp-set-property` events for these attributes:
 - `lang` to propagate a language change (possible values `en`, `de`)
 - `requested-login-status` (possible values `logged-in`, `logged-out`)
 
+### Emitted events
+
+#### dbp-lang
+
+The component emits a `dbp-lang` event when the language is changed (for example in the language picker).
+The `details` attribute of the event is the language (possible values `en`, `de`).
+
 ## Topic Metadata
 
 ```json

packages/app-shell/src/app-shell.js

@@ -296,6 +296,14 @@ export class AppShell extends ScopedElementsMixin(AdapterLitElement) {
                     this.router.update();
                     this.subtitle = this.activeMetaDataText("short_name");
                     this.description = this.activeMetaDataText("description");
+
+                    // send a dbp-lang event with the language
+                    const event = new CustomEvent('dbp-lang', {
+                        bubbles: true,
+                        composed: true,
+                        detail: this.lang
+                    });
+                    this.dispatchEvent(event);
                 break;
                 case 'metadata':
                 {