Steps to reproduce:

1. switch Confluence to the Italian language (other languages seem ok)
2. navigate to any page
3. ensure the sidebar is shown (if hidden the bug doesn't happen)
4. click on the "Condividi" ("Share") button
5. enter a username or an email address and confirm it

At this point the share popup box will move over the right edge of your browser (it actually seems to vanish).

Even before the step 5, you can see something strange: the DOM element div#inline-dialog-shareContentPopup has the CSS property "left: 846.933px;", while in other cases it has "left: auto; right: 10px;".
After the step 5, the "left" property gets increased of about 300px, so that the popup "disappears".