Inconsistencies of the behaviour of QLocale, and no respect to system's local

Hi !

Qt core seems to correctly detect system local, but it seems to incorrectly respect it.

#include <qapplication.h>
#include <qpushbutton.h>

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

    QPushButton hello( "Hello world!");
    hello.resize( 100, 30 );
    hello.show();

    QString test;
    test = QLocale::system().toString(0.5);// ==> 0.5       MARK2
    test = QLocale::system().name();       // ==> fr_FR     MARK1
    test = QLocale().toString(0.5);        // ==> 0.5
    test = QLocale(QLocale::system().name()).toString(0.5);  // ==> 0,5   expected value ! MARK3
    QLocale locale = QLocale(QLocale::French, QLocale::France);
    test = locale.toString(0.5);           // ==> 0,5   expected value !
    QLocale::setDefault(QLocale(QLocale::French, QLocale::France));
    test = QLocale().toString(0.5);        // ==> 0,5   expected value !

    return a.exec();
}

As you can see on MARK1, my system's local is correctly detected but as illustrated on MARK2 Qt doesn't respect it: it should have display 0,5 (and not 0.5).

I worked the problem and saw that :

• by using directly an instance of QLocale (initialized with fr_FR), all is correct
• when using a console application, there is no problem whatsoever; here an extract of the .pro file

  QT -= gui
  
  CONFIG += c++11 console
  CONFIG -= app_bundle
  

• this problem may be connected to the following tickets : 58504,  63324

the ldd on the binary:

linux-vdso.so.1 (0x00007ffeefaf9000)
libQt5Widgets.so.5 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libQt5Widgets.so.5 (0x00007f7a384bf000)
libQt5Gui.so.5 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libQt5Gui.so.5 (0x00007f7a37cd8000)
libQt5Core.so.5 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libQt5Core.so.5 (0x00007f7a37588000)
libGL.so.1 => /usr/lib/x86_64-linux-gnu/libGL.so.1 (0x00007f7a372fc000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f7a370de000)
libstdc+.so.6 => /usr/lib/x86_64-linux-gnu/libstdc+.so.6 (0x00007f7a36d59000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f7a369c6000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f7a367ae000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7a363f4000)
libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f7a361da000)
libicui18n.so.56 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libicui18n.so.56 (0x00007f7a35d41000)
libicuuc.so.56 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libicuuc.so.56 (0x00007f7a35989000)
libicudata.so.56 => /home/hide/.root/Applications/Qt/5.10.1/gcc_64/lib/libicudata.so.56 (0x00007f7a33fa6000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7a33da2000)
libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f7a33ba0000)
libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f7a3388a000)
/lib64/ld-linux-x86-64.so.2 (0x00007f7a38f00000)
libGLX.so.0 => /usr/lib/x86_64-linux-gnu/libGLX.so.0 (0x00007f7a33659000)
libGLdispatch.so.0 => /usr/lib/x86_64-linux-gnu/libGLdispatch.so.0 (0x00007f7a333a3000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f7a33131000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007f7a32df1000)
libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007f7a32bdf000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007f7a329b7000)
libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007f7a327b3000)
libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007f7a325ad000)
libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007f7a32398000)
librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f7a32190000)