The Locale setting in Tools->Options->Language Settings->Languages is not saved. Every time LibreOffice is started, the selected locale setting is reset back to the same language as the setting for "User interface". E.g. if I set the user interface language to "English (USA)" and the locale to "Swedish (Sweden)", the locale will be set to "English (USA)" the next time I start LibreOffice.
Further tests have showed that this bug is only present i LibreOffice Portable from portableapps.com, so I've changed the status to "not our bug".
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.