loading qm file using QTranslator

I'm trying to use translation files. I went through all the procedures: created ts file, translated it, but when I run the application, the language is still the same as before.

I worked on the Nokia example, just like in the instructions.

What could be my problem?

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QTranslator* translator=new QTranslator(0);

    if(QFile::exists("hellotr_la.qm"))
        qWarning("failed-no file");

    if(! translator->load("hellotr_la.qm"))
        qWarning("failed loading"); //the warning appears ****

    app.installTranslator(translator);
}