Returns supported language pairs.
This info may be used by other plugins to find out what language pairs can handle the translator.
\Drupal\tmgmt\TranslatorInterface $translator: The translator entity.
array List of language pairs where a pair is an associative array of source_language and target_language. Example: array( array('source_language' => 'en-US', 'target_language' => 'de-DE'), array('source_language' => 'en-US', 'target_language' => 'de-CH'), )
public function getSupportedLanguagePairs(TranslatorInterface $translator);