FluentValidation comes with errors localized into several different languages. You don't need to include these satellite assemblies in your own project though - just remove the other culture folders from the directory where you're referencing the FV dll from.
If you want to use your own resources you'll need to set the resource provider type. See this page in the docs: http://fluentvalidation.codeplex.com/wikipage?title=Localization&referringTitle=Documentation
Jeremy