Node.js Translate

1. Install as you would normally install a contributed Drupal module.
2. You also need to install Node.js:
   https://nodejs.org/en
3. And run these commands in libraries/google-translate folder:
   

   npm install
   npm start

4. Node.js Translate service will work only if your terminal is working.
   If you need to run it automatically, use PM2 to run process in background
   and startup it automatically.

   npm install pm2@latest -g
   yarn global add pm2
   pm2 start index.js
   pm2 save

Before start translation, you need to run node.js service
on your local server or use external server.
If you use external server, then you will need
to update IP address on configuration form:

/admin/config/regional/nodejs_translate

Also, increase delay time between requests for long texts,
and decrease delay time for short texts like taxonomy term names.

Nodejs Translate has settings for multiple hosts for translations. Hosts will be used one by one alternately, so you can decrease delay between translations using multiple servers with different IP addresses.

Node.js Translate provides single and multiple translation
drush commands:

Single Translate

Single translate command can translate only one entity.
You also need to pass Entity Type ID as first argument.

nodejs_translate:single_translate entity_type_id entity_id

entity_type_id - node, block_content, taxonomy_term, etc.
entity_id - nid, block id, tid, etc.

Usage:

nodejs_translate:single_translate node 42

alias nodejs-st

nodejs-st node 42

Multiple Translate

Multiple translate command can translate all entities
for one bundle (node type, taxonomy vocabulary, block type).
You need to pass Entity Type ID and Bundle in drush command.

nodejs_translate:multiple_translate entity_type_id bundle

Usage:

nodejs_translate:single_translate node article

alias:
nodejs-mt

nodejs-mt node article

Use getTranslation() method to translate short stings or texts:

\Drupal::service('nodejs_translate.nodejs_translator')->getTranslation($string, $from, $to)

Use translateText() method to translate texts longer than 4000 characters:

\Drupal::service('nodejs_translate.nodejs_translator')->translateText($text, $from, $to)

Use hook_nodejs_translate_languages_alter() hook to map your Drupal langcodes with ISO-639 language codes.
https://cloud.google.com/translate/docs/languages

function hook_nodejs_translate_languages_alter(string &$languages) {
  // @see https://cloud.google.com/translate/docs/languages for ISO-639 codes.
  $languages['zh_hans'] = 'zh';
  $languages['pt_pt'] = 'pt';
}

For adding fields to translations use hook_nodejs_translate_entity_alter() hook:

function hook_nodejs_translate_entity_alter(&$entity_translated, $entity_original, $source_language, $destination_language) {
  if ($entity_translated->hasField('field_text')) {
    $text_translated = \Drupal::service('nodejs_translate.nodejs_translator')->translateText($entity_original->field_text->value, $source_language, $destination_language);
    $entity_translated->field_text->value = $text_translated;
    $entity_translated->field_text->format = $entity_original->field_text->format;
  }
}

You can run translate for big texts and need to split HTML/text in chunks
less than 4900 characters. And you need to set up delay between
each translation. Delays must be different, it can't be the same,
because we need to pretend real user behaviour. Node.js Translate has
configuration for delay values.
Also, I couldn't find smart split on chunks to support right splitting
without cutting HTML tags in the middle. Feel free to suggest smart split
library in the module issues.
More about quotas read here:
https://cloud.google.com/translate/quotas