photoviewer: Use QLocale::uiLanguages() for finding translations

Now that we ship en translations, we can use the
QTranslator::load(QLocale, ...) overload to correctly find translated
files.

See 785b12a4d126 for the corresponding change in qtdeclarative/5.11.

Task-number: QTBUG-69196
Change-Id: Ic7f7a2c70763f0c7200782d6e46644f2b3f7f3ef
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

examples/demos/photoviewer/main.cpp

@@ -58,7 +58,7 @@ int main(int argc, char *argv[])
     QGuiApplication app(argc, argv);
 
     QTranslator qtTranslator;
-    qtTranslator.load("qml_" + QLocale::system().name(), ":/i18n/");
+    qtTranslator.load(QLocale(), "qml", "_", ":/i18n/");
     app.installTranslator(&qtTranslator);
 
     QQmlApplicationEngine engine;