How to change locale

[memus]

Hi there,
i have problem with QLocale.
When i try to set other locale:

QLocale::setDefault(QLocale::English, QLocale::UnitedStates);
qDebug() << QLocale::system().language();

QLocale::setDefault(QLocale::English, QLocale::UnitedStates);
qDebug() << QLocale::system().language();

To copy to clipboard, switch view to plain text mode 

Output should be 31 but is 90 (my locale). Why?