feat(transcription): Adds additional languages via metadata.

src/main/java/org/jitsi/jigasi/JvbConference.java

@@ -2216,6 +2216,14 @@ private void processRoomMetadataJson(String json)
                     JSONObject recordingObj = (JSONObject)metadataObj.getOrDefault("recording", new JSONObject());
                     ((TranscriptionGatewaySession)this.gatewaySession).setBackendTranscribingEnabled(
                         (boolean)recordingObj.getOrDefault("isTranscribingEnabled", false));
+
+                    JSONObject visitorsObj = (JSONObject)metadataObj.getOrDefault("visitors", new JSONObject());
+                    String languages = (String)visitorsObj.get("transcribingLanguages");
+                    if (StringUtils.isNotEmpty(languages))
+                    {
+                        ((TranscriptionGatewaySession)this.gatewaySession)
+                                .updateTranslateLanguages(languages.split(","));
+                    }
                 }
             }
         }

src/main/java/org/jitsi/jigasi/TranscriptionGatewaySession.java

@@ -126,6 +126,12 @@ public class TranscriptionGatewaySession
      */
     private int numberOfScheduledParticipantsLeaving = 0;
 
+    /**
+     * The currently used additional languages for translation.
+     * Used for visitors to announce the languages used by visitors.
+     */
+    private List<String> additionalLanguages = new ArrayList<>();
+
     /**
      * Create a TranscriptionGatewaySession which can handle the transcription
      * of a JVB conference
@@ -753,4 +759,22 @@ public void setBackendTranscribingEnabled(boolean backendTranscribingEnabled)
 
         this.maybeStopTranscription();
     }
+
+    /**
+     * To update all participant languages with the additional that are provided.
+     * @param additionalLanguages languages to add to those from the participants.
+     */
+    void updateTranslateLanguages(String[] additionalLanguages)
+    {
+        List<String> oldLangs = this.additionalLanguages;
+        this.additionalLanguages = Arrays.asList(additionalLanguages);
+
+        // remove unused streams
+        oldLangs.stream().filter(s -> !this.additionalLanguages.contains(s))
+            .forEach(lang -> this.transcriber.getTranslationManager().removeLanguage(lang));
+
+        // add new languages
+        this.additionalLanguages.stream().filter(s -> !oldLangs.contains(s))
+            .forEach(lang -> this.transcriber.getTranslationManager().addLanguage(lang));
+    }
 }

src/main/java/org/jitsi/jigasi/transcription/Transcriber.java

@@ -834,6 +834,14 @@ public TranscriptionService getTranscriptionService()
         return transcriptionService;
     }
 
+    /**
+     * @return the {@link TranslationManager}.
+     */
+    public TranslationManager getTranslationManager()
+    {
+        return this.translationManager;
+    }
+
     /**
      * Notifies all of the listeners of this {@link Transcriber} of a new
      * {@link TranscriptionResult} which was received.

src/main/java/org/jitsi/jigasi/transcription/TranslationManager.java

@@ -140,9 +140,15 @@ private List<TranslationResult> getTranslations(
         {
             for (String targetLanguage : translationLanguages)
             {
+                String sourceLang = result.getParticipant().getSourceLanguage();
+                if (sourceLang != null && sourceLang.equals(targetLanguage))
+                {
+                    continue;
+                }
+
                 String translatedText = translationService.translate(
                     alternatives.iterator().next().getTranscription(),
-                    result.getParticipant().getSourceLanguage(),
+                    sourceLang,
                     targetLanguage);
 
                 translatedResults.add(new TranslationResult(