If a catalog with full language name ("fr_BE") doesn't exist,
wxFileTranslationsLoader tries to look for just the base language ("fr")
too. This isn't something specific to wxFileTranslationsLoader, it makes
sense to do it regardless of the loader.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64154 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775