In v5.0 (and v5.0.1), there is an error in French language file (fr.xml) which causes blank login page when this language is selected.
Please download the fixed french language file
and put this file to FileVista\App_GlobalResources\FileVistaResourceStore\Languages folder. This will override the bundled French language file with the fixed one.
In the next minor release, this fixed language file will be automatically included.