Your configuration is all right.
I'm not sure whether this could cause the problem, but the ordering of your first several plugins is set to zero. Just to be sure, try setting the System - ARTIO JoomSEF ordering for example to -1. You need to click the Ordering column title to be able to modify and save the ordering value - see attached screenshot as an example.



Of course after you change it make sure that you delete the already created SEF URLs with wrong meta data using JoomSEF's URLs Manager and clear JoomSEF's cache, so the URLs can be recreated with current settings.

Thanks for the suggestion,
unfortunately, after having followed the instructions you sent me, the problem is still here.
When i browse a page that has been translated in French, inspecting the source code I can still see the metadata tags description and keywords of the page in english.
It does not matter in the end is not a serious problem...
In my opinion it works best the solution adopted on the 3.9 version of JoomSEF with Joom!Fish, in that case the metadata tags where left empty.
In any case I want to thank you for the support
Alex