The Locale setting in Tools->Options->Language Settings->Languages is not
saved when the locale is different from the user interface language. 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.
This bug is specific to the portable version, see http://en.libreofficeforum.org/node/327