The new version improves compatibility. The automatic switch to Compatibility Mode for several plugins was removed because this caused some other problems. At the same time support for WPML and Polylang was enhanced. The admin message which lead to some confusion was completely discarded.
The selected 404 page now is automatically excluded from search – for all languages if WPML or Polylang is active. Also it is excluded from page lists. This should remove the 404 page e.g. from your sitemap (if the plugin you are using to create the sitemap uses the WordPress function
get_pages). Naturally also for all languages.
This version also fixes a problem combined with author archive pages if a author has no posts.
Plus it includes some functions that can be used by developers to add native support for the 404page plugin to themes (read more).