feat(dynamic-branding) support setting transcription language

It will be used as the default if specified.

react/features/base/conference/functions.ts

@@ -208,6 +208,7 @@ export function getConferenceOptions(stateful: IStateful) {
 
     const config = state['features/base/config'];
     const { locationURL } = state['features/base/connection'];
+    const { defaultTranscriptionLanguage } = state['features/dynamic-branding'];
     const { tenant } = state['features/base/jwt'];
     const { email, name: nick } = getLocalParticipant(state) ?? {};
     const options: any = { ...config };
@@ -229,7 +230,8 @@ export function getConferenceOptions(stateful: IStateful) {
     }
 
     options.applicationName = getName();
-    options.transcriptionLanguage = determineTranscriptionLanguage(options);
+    options.transcriptionLanguage
+        = defaultTranscriptionLanguage ?? determineTranscriptionLanguage(options);
 
     // Disable analytics, if requested.
     if (options.disableThirdPartyRequests) {

react/features/base/i18n/middleware.ts

@@ -1,4 +1,5 @@
 import { SET_DYNAMIC_BRANDING_DATA } from '../../dynamic-branding/actionTypes';
+import { getConferenceState } from '../conference/functions';
 import MiddlewareRegistry from '../redux/MiddlewareRegistry';
 
 import { I18NEXT_INITIALIZED, LANGUAGE_CHANGED } from './actionTypes';
@@ -28,6 +29,18 @@ MiddlewareRegistry.register(store => next => action => {
                 logger.log('Error setting dynamic language bundle', err);
             });
         }
+
+        // Update transcription language, if applicable.
+        if (action.type === SET_DYNAMIC_BRANDING_DATA) {
+            const { defaultTranscriptionLanguage } = action.value;
+
+            if (typeof defaultTranscriptionLanguage !== 'undefined') {
+                const { conference } = getConferenceState(store.getState());
+
+                conference?.setTranscriptionLanguage(defaultTranscriptionLanguage);
+            }
+        }
+
         break;
     }
     }

react/features/dynamic-branding/reducer.ts

@@ -150,6 +150,7 @@ export interface IDynamicBrandingState {
     customizationFailed: boolean;
     customizationReady: boolean;
     defaultBranding: boolean;
+    defaultTranscriptionLanguage?: boolean;
     didPageUrl: string;
     inviteDomain: string;
     labels: Object | null;