You should always use the resource manager and not read files directly to ensure globalization is taken into account.
using System.Collections;
using System.Globalization;
using System.Resources;
...
/* Reference to your resources class -- may be named differently in your case */
ResourceManager MyResourceClass =
new ResourceManager(typeof(Resources));
ResourceSet resourceSet =
MyResourceClass.ResourceManager.GetResourceSet(CultureInfo.CurrentUICulture, true, true);
foreach (DictionaryEntry entry in resourceSet)
{
string resourceKey = entry.Key.ToString();
object resource = entry.Value;
}