I added an extra translatable field in the categories called “Description 2” but I’m having trouble using the WYSIWYG editor on that field.
I use Prestashop 1.7.8.8 with Elementor addon and there are 4 active languages

    use PrestaShopBundleFormAdminTypeFormattedTextareaType;
    use PrestaShopBundleFormAdminTypeTranslatableType;
    use SymfonyComponentFormExtensionCoreTypeTextareaType;

    public function hookActionCategoryFormBuilderModifier(array $params)
    {
        /** @var SymfonyComponentFormFormBuilder $formBuilder */
        $formBuilder = $params['form_builder'];
 
        $formBuilder->add('description_short',
            // cf. https://devdocs.prestashop.com/1.7/development/components/form/types-reference/
            TranslatableType::class,
            [
                'label' => $this->l('Descrizione 2'),
                'required' => false,
                'type' => TextAreaType::class
            ]
        );

        /*
        $formBuilder
            ->add('description_2', TranslatableType::class, [
                'label' => $this->l('Descrizione 2'),
                'type' => FormattedTextareaType::class,
                'required' => false
            ]);
        */

        $category = new Category((int)$params['id']);
        $params['data']['description_2'] = $category->description_2;
 
        $formBuilder->setData($params['data']);
    }

i get this