Set default language to English (en-US)

[neozhu]

Localization Configuration Update

Changes

• Set default language to English (en-US)
• Added clear documentation for DefaultLanguageCode
• Simplified language code annotation

public static class LocalizationConstants
{
    public const string ResourcesPath = "Resources";
    /// <summary>
    /// Default language code. Set to English (en-US). 
    /// Change to "zh-CN" for Chinese or other codes from SupportedLanguages.
    /// </summary>
    public const string DefaultLanguageCode = "en-US";

   ...
}