Tor Browser before 8.0.1 has an information exposure vulnerability. It allows remote attackers to detect the browser's UI locale by measuring a button width, even if the user has a "Don't send my language" setting.
https://trac.torproject.org/projects/tor/ticket/24056
https://hackerone.com/reports/282748
https://gitweb.torproject.org/tor-browser.git/commit/?id=cbb04b72c68272c2de42f157d40cd7d29a6b7b55