There is a typo in the pot available in translate.fedoraproject.org (aka Transifex) : https://translate.fedoraproject.org/POT/packagekit.master/packagekit.master.pot
The following string :
#. TRANSLATORS: This a prompt asking the user to import the security key
msgid "You you accept this signature?"
should be : "Do you accept this signature?"
Fixed, many thanks.