code: @Override
      public DescribeVoicesResult describeVoices(DescribeVoicesRequest request) {
          request = beforeClientExecution(request);
          return executeDescribeVoices(request);
      }
docs: <p>
  Returns the list of voices that are available for use when requesting speech synthesis. Each voice speaks a
  specified language, is either male or female, and is identified by an ID, which is the ASCII version of the voice
  name.
  </p>
  <p>
  When synthesizing speech ( <code>SynthesizeSpeech</code> ), you provide the voice ID for the voice you want from
  the list of voices returned by <code>DescribeVoices</code>.
  </p>
  <p>
  For example, you want your news reader application to read news in a specific language, but giving a user the
  option to choose the voice. Using the <code>DescribeVoices</code> operation you can provide the user with a list
  of available voices to select from.
  </p>
  <p>
  You can optionally specify a language code to filter the available voices. For example, if you specify
  <code>en-US</code>, the operation returns a list of all available US English voices.
  </p>
  <p>
  This operation requires permissions to perform the <code>polly:DescribeVoices</code> action.
  </p>
  
  @param describeVoicesRequest
  @return Result of the DescribeVoices operation returned by the service.
  @throws InvalidNextTokenException
  The NextToken is invalid. Verify that it's spelled correctly, and then try again.
  @throws ServiceFailureException
  An unknown condition has caused a service failure.
  @sample AmazonPolly.DescribeVoices
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/polly-2016-06-10/DescribeVoices" target="_top">AWS API
  Documentation</a>