function themename_preprocess(&$variables) {
   $block = DrupalblockEntityBlock::load('language_block');
   $variables['block_output'] = Drupal::entityTypeManager()->getViewBuilder('block') ->view($block);

   echo $variables['block_output'];
   exit;
}

TypeError: Argument 1 passed to DrupalblockBlockViewBuilder::view() must implement interface DrupalCoreEntityEntityInterface, null given,