translateFilterLoadStrings example

'#tree' => TRUE,
      '#language' => $langname,
      '#header' => [
        $this->t('Source string'),
        $this->t('Translation for @language', ['@language' => $langname]),
      ],
      '#empty' => $this->t('No strings available.'),
      '#attributes' => ['class' => ['locale-translate-edit-table']],
    ];

    if (isset($langcode)) {
      $strings = $this->translateFilterLoadStrings();

      $plurals = $this->getNumberOfPlurals($langcode);

      foreach ($strings as $string) {
        // Cast into source string, will do for our purposes.         $source = new SourceString($string);
        // Split source to work with plural values.         $source_array = $source->getPlurals();
        $translation_array = $string->getPlurals();
        if (count($source_array) == 1) {
          // Add original string value and mark as non-plural.