Qt C++ How to get locale language ?

Gilboonet

Hello, my C++ application works but it's only in my language which is french. I'm trying to make it appear in English when user's locale is not french. I used QT Linguist and create two .tr files, one for french and another one for english, then I created the .qm files and now I'm trying to use those .qm files into my main function that is now :

#include "mainwindow.h"

#include <QApplication>
#include <QTranslator>

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

    QTranslator translator;
    QLocale locale = QLocale();
    QString lang = QLocale::languageToString(locale.language());
    qInfo() << locale;
    if (translator.load(QLocale(), lang == "French" ? "UI1_fr.qm" : "UI1_en.qm"))
        QApplication::installTranslator(&translator);

    MainWindow w;
    w.show();
    return a.exec();
}

To test I changed my system language to English but my code always shows "French" as language string. Maybe

QLocale locale = QLocale();

is not the good way to retrieve the system locale ? Or maybe do I need to restart the system (I'm on Ubuntu 22.04 and will also test on Windows 11) ?

Gilboonet

Well, with your help I was able to make it work. I needed to replace
":/Translations"
by
"Translations"

I don't know the meaning of the ":/" at the beginning of the string, (maybe does it mean "from the current directory" ?) but without it it worked.

here's my working main()

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

    QTranslator translator;

    // fichier de la forme ":/Translations/App_xx.qm"
    QString tr_folder="Translations";
    QString tr_file="UI1_"+QLocale::system().name();

    if(translator.load(tr_file,tr_folder))
        QApplication::installTranslator(&translator);
    else
    {	// pas trouvé
     qCritical("\"%s\" file not Found. No translation will occur.",qPrintable(tr_folder+"/"+tr_file));
    }

    MainWindow w;
    w.show();
    return a.exec();
}

mzimmers

@Gilboonet well, what is your system's locale? And, if you want to change that for your application, you can use the set default method.

Gilboonet

@mzimmers I'm not willing to change my locale at runtime, only read what is the default locale and if it's french load the french .qm otherwise load the english .qm

@mzimmers I just reboot and after that, my system's locale (which I changed from French to English) was correctly retrieved. But my Application is still in french, so I supposed I did something wrong with QT Linguist.

Here's what I did with QT Linguist :

edit each string (mainly menus entries) and translate them
save the .tr file

And from the C++ project, I used Tools/Extern/Linguist/lrelease

SGaist

Hi,

Just in case, you don't do anything if the translator load method fails. You should at least print that something went wrong.

SGaist

On a side note, you are not building the file path correctly. See the load method you are using documentation .

mpergand

Hi @Gilboonet

Here the code that I'm using:

// fichier de la forme ":/Translations/App_xx.qm"
QString tr_folder=":/Translations";
QString tr_file="App_"+QLocale::system().name();
	translator=new QTranslator(this);

if(translator->load(tr_file,tr_folder))
    installTranslator(translator);
else
{	// pas trouvé
 qCritical("\"%s\" file not Found. No translation will occur.",qPrintable(tr_folder+"/"+tr_file));
}

Gilboonet

@SGaist You are right, the load method fails and it's because I didn't follow the rules that are stated on the documentation, I was thinking it only needs a file name.

Gilboonet

Well, with your help I was able to make it work. I needed to replace
":/Translations"
by
"Translations"

I don't know the meaning of the ":/" at the beginning of the string, (maybe does it mean "from the current directory" ?) but without it it worked.

here's my working main()

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

    QTranslator translator;

    // fichier de la forme ":/Translations/App_xx.qm"
    QString tr_folder="Translations";
    QString tr_file="UI1_"+QLocale::system().name();

    if(translator.load(tr_file,tr_folder))
        QApplication::installTranslator(&translator);
    else
    {	// pas trouvé
     qCritical("\"%s\" file not Found. No translation will occur.",qPrintable(tr_folder+"/"+tr_file));
    }

    MainWindow w;
    w.show();
    return a.exec();
}

SGaist

The ":/" is the root of Qt's resource system path.