Another minor issue: after restoring my tabs (tabs and tabpermission tables) I could restore site's functionalities, but I now see admin tabs showing the old "Visible By Administrators Only" message in red. What's the way to remove it?

 Luiz,
yes I already checked and values are correct (administratorroleid=0, registeredroleid=1, corresponding to values in roles table).
What I noted is that my Tabs table has different values for the culturecode field: sometimes null, sometimes en-us and sometimes it-it: could this be the cause of those problems with the recycle bin?

 Sebastian,
I manually updated culturecode, setting en-us where it was it-it, and all continues to work properly. But having default portal language set to italian, new pages are created with that culture: should I always manually update? What could be the risk if I do not do that?

I also performed a new upgrade to 5.4.1 on a couple of hosts, and noticed that on the one with problems (loosing admin tabs) I have three records in PortalLocalization: one for en-us culture, one for it-it and an empty one. 
Viceversa, on the other host I only have two for the two locales: could it be that empty value causing problems?