Hello,
Contact plugin author and ask if they have a shortcode of the language selector. You’ll be able to add the shortcode to the header using header builder Custom HTML block or using Widgets element.
I checked your single product page and unfortunately, it’s not possible to place “(OU) SÉLECTION MANUELLE…” text next to q-ty with the existing HTML structure. You may submit additional customization request to WPKraken team. Maybe they will be able to help you because we are unable to provide support for customizations under our Support Policy.
Add the below code to center the image
.template-container .woocommerce-product-gallery.images-wrapper, .template-container .woocommerce-product-gallery img {
margin: auto;
}
Regards