This plugin is not properly prepared for localization…

This pluginPlugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party is not properly prepared for localizationLocalization Localization (sometimes shortened to "l10n") is the process of adapting a product or service to a particular language, culture, and desired local "look-and-feel.". If you would like to translate this plugin, please contact the author.

How should I prepare my plugin for translation?
https://wordpress.org/plugins/bbpress-new-ui/