Work around layouting issue for RTL languages

This has been fixed in the meanwhile, but we are still shipping
with Qt 5.4. Also, some Linux Distros will still have older Qt
versions.

Addresses issue #4301

src/gui/application.cpp

@@ -570,6 +570,10 @@ void Application::setupTranslations()
         if (property("ui_lang").isNull())
             setProperty("ui_lang", "C");
     }
+// Work around Qt 5 < 5.5.0 regression, see https://bugreports.qt.io/browse/QTBUG-43447
+#if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0) && QT_VERSION < QT_VERSION_CHECK(5, 5, 0)
+    setLayoutDirection(QApplication::tr("QT_LAYOUT_DIRECTION") == QLatin1String("RTL") ? Qt::RightToLeft : Qt::LeftToRight);
+#endif
 }
 
 bool Application::giveHelp()