GUI - further locale discovery tweaks

Now Windows 10 appears to behave similarly to macOS Big Sur.

Author: samaaron

app/gui/qt/main.cpp

@@ -49,14 +49,14 @@ int main(int argc, char *argv[])
 
   qRegisterMetaType<SonicPiLog::MultiMessage>("SonicPiLog::MultiMessage");
 
-  QString systemLocale = QLocale::system().uiLanguages()[0];
+  QString systemLocale = QLocale::system().uiLanguages()[0].replace("-", "_");
 
   QTranslator qtTranslator;
   qtTranslator.load("qt_" + systemLocale, QLibraryInfo::location(QLibraryInfo::TranslationsPath));
   app.installTranslator(&qtTranslator);
 
   QTranslator translator;
-  bool i18n = translator.load(QLocale(), QLatin1String("sonic-pi"), QLatin1String("_"), QLatin1String(":/lang")) ||  systemLocale.startsWith("en") || systemLocale == "C";
+  bool i18n = translator.load(QLatin1String("sonic-pi_") + systemLocale, QLatin1String(":/lang")) ||  systemLocale.startsWith("en") || systemLocale == "C";
   app.installTranslator(&translator);
 
   app.setApplicationName(QObject::tr("Sonic Pi"));