AWS Chime Meeting transcription - EngineTranscribeSettings

Hello,

I would like to start meeting transcription with automatic language detection. According to the documentation link, I set up the configuration:

StartMeetingTranscriptionCommand({
      MeetingId: meetingId,
      TranscriptionConfiguration: {
        EngineTranscribeSettings: {
          IdentifyLanguage: true,
          LanguageOptions: "en-US,de-DE",
          Region: 'us-east-1',
          EnableChannelIdentification: true
        }
      }
    });

When I execute the command I see error

 "message": "1 validation error detected: Value null at 'transcriptionConfiguration.engineTranscribeSettings.languageCode' failed to satisfy constraint: Member must not be null"

In the docs I see that this field is not required.

Where is the issue? I would be grateful for any suggestion.