Thiago mentioned that QDate should not be localized[1]. Thus, the below related functions from QDate class[2] should not use localized names.

QString 	longDayName ( int weekday, MonthNameType type )
QString 	longMonthName ( int month, MonthNameType type )
QString 	shortDayName ( int weekday, MonthNameType type )
QString 	shortMonthName ( int month, MonthNameType type )

We have missed to change that in Qt 5. This issue reported to remind us to change it in the future releases.

[1] https://codereview.qt-project.org/#change,42602
[2] http://doc.qt.digia.com/qt/qdate.html