string en = resourceManager.GetString("MyString", new CultureInfo("en"));
string es = resourceManager.GetString("MyString", new CultureInfo("es"));

//compare here
	
ResourceManager resourceManager = new ResourceManager(typeof(Strings));
IEnumerable<string> neutralResourceNames = resourceManager.GetResourceSet(CultureInfo.InvariantCulture, true, false)
    .Cast<DictionaryEntry>().Select(entry => (string)entry.Key);
IEnumerable<string> localizedResourceNames = resourceManager.GetResourceSet(new CultureInfo("es"), true, false)
    .Cast<DictionaryEntry>().Select(entry => (string)entry.Key);

Console.WriteLine("Missing localized resources:");
foreach (string name in neutralResourceNames.Except(localizedResourceNames))
{
    Console.WriteLine(name);
}

Console.WriteLine("Extra localized resources:");
foreach (string name in localizedResourceNames.Except(neutralResourceNames))
{
    Console.WriteLine(name);
}