Hi Matthew,
Thanks for the update.
This time,I managed to install the plugin, however when trying to activate the subdirectory structure (one language per subdirectory), I get no result. I disactivated the language picker. I visited the permalink page.
I also notices that the hreflang annottaion is not properly implemented, and I get something like:
https://fr/www.mysite.co.uk/”
Thanks again for the help.