Create custom Symfony translation extractor

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Overview

The Symfony translation component allows you to extract translations from your PHP codebase & Twig templates into the translation file format of your liking, for example .po files.

The documentation describes it like this:

The most time-consuming tasks when translating an application is to extract all the template contents to be translated and to keep all the translation files in sync. Symfony includes a command called translation:update that helps you with these tasks.

But what if not all my translations are hardcoded in code or templates, and some - or all - are dynamic? For example loaded from an external data source, like a REST API.

Create translation extractor

You can add your own translation extractor. Which will be run when executing the Symfony consoles’ translation:update command. In addition to the extractors that are already included.

Create a class that implements the ExtractorInterface:

<?php

declare(strict_types=1);

namespace App\Translation;

use Symfony\Component\Translation\Extractor\ExtractorInterface;
use Symfony\Component\Translation\MessageCatalogue;

/**
 * Extracts custom translation strings.
 *
 * @package App\Translation
 */
class TranslationsExtractor implements ExtractorInterface {

  /**
   * Prefix for new found message.
   *
   * @var string
   */
  private $prefix = '';

  /**
   * Returns the translation messages.
   *
   * @return string[]
   *   All messages.
   */
  protected function getMessages(): array {
    $messages = [];

    // TODO: Get all your translation strings here.
    return $messages;
  }

  /**
   * Extracts translation messages to the catalogue.
   *
   * @param string|array $resource
   *   Files, a file or a directory.
   * @param \Symfony\Component\Translation\MessageCatalogue $catalogue
   *   The message catalogue.
   */
  public function extract($resource, MessageCatalogue $catalogue) {
    foreach ($this->getMessages() as $message) {
      $catalogue->set($message, $this->prefix . $message);
    }
  }

  /**
   * {@inheritdoc}
   */
  public function setPrefix(string $prefix) {
    $this->prefix = $prefix;
  }

}

Tag it with name=translation.extractor & an alias.

# config/services.yml
services:
  translation.translations_extractor:
    class: App\Translation\TranslationsExtractor
    tags:
      - { name: translation.extractor, alias: custom }

This was written using Symfony version 5.1.6.