Right now, the script only parses gettext calls where the text domain matches the plugin slug by setting $this->translations->setDomain( $this->slug ).

This matches WordPress.org behaviour, see https://developer.wordpress.org/plugins/internationalization/how-to-internationalize-your-plugin/.

However, sometimes developers include third-party libraries in their plugins with different text domains and still expect those to be extracted.

Since I'd like to keep the current behaviour as the default, maybe we can add an --ignore-domain option to the script?

The code could look like this (simplified):

if ( ! Utils\get_flag_value( $assoc_args, 'ignore-domain' ) {
    $this->translations->setDomain( $this->slug );
}