Our plugin is 100% translated in Dutch, but only for nl_NL, therefore, for another Dutch locales (e.g. nl_BE, nl_NL_formal), you would need to download the translation files from 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:
