Textarea.php

<?php

namespace Drupal\config_translation\FormElement;

use Drupal\Core\Language\LanguageInterface;

/**
 * Defines the textarea element for the configuration translation interface.
 */
class Textarea extends FormElementBase {
    
    /**
     * {@inheritdoc}
     */
    public function getTranslationElement(LanguageInterface $translation_language, $source_config, $translation_config) {
        // Estimate a comfortable size of the input textarea.
        $rows_words = ceil(str_word_count($translation_config) / 5);
        $rows_newlines = substr_count($translation_config, "\n") + 1;
        $rows = max($rows_words, $rows_newlines);
        return [
            '#type' => 'textarea',
            '#rows' => $rows,
        ] + parent::getTranslationElement($translation_language, $source_config, $translation_config);
    }

}