'image_alternative' => [
          '#type' => 'inline_template',
          '#template' => '<a href="#" class="cke-icon-only" role="button" title="' . $this->t('Language') . '" aria-label="' . $this->t('Language') . '"><span class="cke_button_icon cke_button__language_icon">' . $this->t('Language') . '</span></a>',
        ],

$build = new \Drupal\Component\Render\FormattableMarkup('@name', [
  '@name' => 'test',
]); echo (string)$build;

$renderer = \Drupal::service('renderer');

$start = microtime(TRUE);
$build = [
  '#type' => 'inline_template',
  '#template' => "{{ 'Тест'|lower }}",
];
$output = $renderer->renderRoot($build);
$end = microtime(TRUE);
echo round(1000 * ($end - $start), 3), " ms\n";