Is it possible to add some value from resource file right into the XAML markup? Or for localization we always have to make something like this in *.cs file:
The simplest way is probably to reference the items directly (they are static properties, internal by default):
If you are working on a localised WPF app though then I'd recommend taking a look at the guidance on CodePlex at http://wpflocalization.codeplex.com/ , and if you're building a composite app (using PRISM or MEF) then I have a blog post on a nice way to accomplish WPF localisation using standard bindings.