cmake-gui: Restore support for internationalization with Qt5 on Windows

Restore the logic removed by commit 035078d847 (cmake-gui: Remove
explicit locale setup, 2020-12-17, v3.20.0-rc1~205^2~6), but only with
Qt5 on Windows.  Leave a FIXME comment to support Qt6 later.

Fixes: #23562
Issue: #23565
1 file changed