qt5_add_big_resources does not support language-dependent resources

According to the documentation (https://doc.qt.io/qt-5/resources.html), the Qt resource system supports resources need to change based on the user's locale. This is done by adding a lang attribute to the qresource tag, specifying a suitable locale string.

While this works fine if I add the *.qrc file as the to the SOURCES of my cmake project, the locale-speficif behaviour fails when I use the CMake macro qt5_add_big_resources. On compilation, I receive a warning ("Possible duplicate alias detected"), and the first-mentioned resource is used indepently of the locate.

I would suggest to either implement locale-speficic behaviour in qt5_add_big_resources, or to add a big warning in the documentation that qt5_add_big_resources does not behaves as expected.