Webengine default locale not transferred to JS

// main.cpp
int main(int argc, char **argv) {
    qputenv("QT_IM_MODULE", QByteArray("qtvirtualkeyboard"));
    
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts);

    QGuiApplication app(argc, argv);

    int num = 1234567890;  QLocale::setDefault(QLocale("de_CH"));
    qDebug() << "locale:" << QLocale().name() << " num:" << QLocale().toString(num);

    QtWebEngine::initialize();
    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("./main.qml")));

    QQuickWindow *window = qobject_cast<QQuickWindow*>(engine.rootObjects().first());

    window->show();
    return app.exec();
}

// main.qml
    Text {
        property var num: 1234567890
        anchors.centerIn: parent        Component.onCompleted: {
            console.log("num2: " + num.toLocaleString(Qt.locale()))
        }
    }    WebEngineView {
        anchors.fill: parent
        profile: profile
        url: "file:///home/andy/DEV/native/projects/QT/egl/html/index.html"
    }    WebEngineProfile {
        id: profile
        httpAcceptLanguage: "de-CH"
    }

application output:
locale: "de_CH"  num: "1'234'567'890"
qml: num2: 1'234'567'890.00

index.html
        
<script type="text/javascript">
    function GetCurrentLocale() {
        console.log("locale: " + navigator.language || navigator.userLanguage);
        var number = 1234567890;
        console.log("number.toLocaleString());
    }
</script>