I guess this section is outdate, because nowadays there's a way to translate PDF documents using several languages through REST requests. But there's a Node example in this page using NodeJs https://cloud.google.com/translate/docs/advanced/translate-documents#translate_batch_translate_document-nodejs

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */
// const projectId = 'YOUR_PROJECT_ID';
// const location = 'us-central1';
// const inputUri = 'path_to_your_files';
// const outputUri = 'path_to_your_output_bucket';

// Imports the Google Cloud Translation library
const {TranslationServiceClient} = require('@google-cloud/translate').v3beta1;

// Instantiates a client
const translationClient = new TranslationServiceClient();

const documentInputConfig = {
  gcsSource: {
    inputUri: inputUri,
  },
};

async function batchTranslateDocument() {
  // Construct request
  const request = {
    parent: translationClient.locationPath(projectId, location),
    documentInputConfig: documentInputConfig,
    sourceLanguageCode: 'en-US',
    targetLanguageCodes: ['sr-Latn'],
    inputConfigs: [
      {
        gcsSource: {
          inputUri: inputUri,
        },
      },
    ],
    outputConfig: {
      gcsDestination: {
        outputUriPrefix: outputUri,
      },
    },
  };

  // Batch translate documents using a long-running operation.
  // You can wait for now, or get results later.
  const [operation] = await translationClient.batchTranslateDocument(request);

  // Wait for operation to complete.
  const [response] = await operation.promise();

  console.log(`Total Pages: ${response.totalPages}`);
}

batchTranslateDocument();