WPML always tests every release with the latest WordPress versions. However, because WPML is not listed in the WordPress repository, it will always show as Compatibility with WordPress: Unknown.
When a new version of WPML is available, it states the compatibility with the latest version of WordPress is unknown. This happens for all plugins that are not available in the WordPress repository, including WPML.
You can rest assured that we thoroughly test each new release with the latest versions of WPML. Please be sure to keep your WPML plugins up to date for the latest security and feature updates.