Hi @nawidkg,
Our plugin is available in Dutch (nl_NL, and nl_NL_formal), but for another Dutch locale (e.g. nl_BE), you will need to download the translation files from Dutch (nl_NL), and manually install it in your site, or even better, use the Dutch (nl_NL) as fallback. There is a great plugin to help you with this: Language Fallback
After installing the plugin, you just need to go to Settings > General, find the Language Fallback Settings and choose Nederlands:

Please note that for the fully translated languages, we don’t bundle the translation projects, but they are managed on https://translate.wordpress.org/ directly.
We only bundle those locales that are partially translated, as WordPress.org requires that the translations be at least 90% complete before creating a language pack. See: https://make.wordpress.org/meta/handbook/tutorials-guides/translations/
Fortunately, translations into Dutch are maintained and updated. You will find the Dutch translations here: https://translate.wordpress.org/locale/nl/default/wp-plugins/woocommerce-pdf-invoices-packing-slips/
After explaining the above, would you consider updating your review? 🙂