Thanks! I'll have a look...

While I'm not using the content finder (I'm using URL rewriting), I am using a custom URL provider so I don't have to worry about prefixing all of my URL's with "/en-us". Here's the implementation if you are curious:

// Namespaces.
using System;
using System.Collections.Generic;
using System.Linq;
using Umbraco.Core.Configuration;
using Umbraco.Core.Logging;
using Umbraco.Web;
using Umbraco.Web.Routing;


/// <summary>
/// Builds international URL's.
/// </summary>
public class InternationalUrlProvider : DefaultUrlProvider
{

    #region Constants

    private const string ErrorBuildingUrl = "Error while attempting to build international URL.";

    #endregion


    #region Constructors

    /// <summary>
    /// Default constructor.
    /// </summary>
    public InternationalUrlProvider() : base(UmbracoConfig.For.UmbracoSettings().RequestHandler)
    {
    }

    #endregion


    #region Public Methods

    /// <summary>
    /// Gets the URL's for other domains.
    /// </summary>
    public override IEnumerable<string> GetOtherUrls(UmbracoContext umbracoContext, int id, Uri current)
    {
        var urls = base.GetOtherUrls(umbracoContext, id, current);
        return urls == null
            ? null
            : urls.Select(x => InternationalizeUrl(x, umbracoContext)).ToList();
    }


    /// <summary>
    /// Gets the main URL.
    /// </summary>
    public override string GetUrl(UmbracoContext umbracoContext, int id, Uri current, UrlProviderMode mode)
    {
        var url = base.GetUrl(umbracoContext, id, current, mode);
        return InternationalizeUrl(url, umbracoContext);
    }

    #endregion


    #region Private Methods

    /// <summary>
    /// Internationalizes a URL.
    /// </summary>
    private string InternationalizeUrl(string url, UmbracoContext umbracoContext)
    {

        // Log errors.
        try
        {
            var validRequest = umbracoContext != null && umbracoContext.HttpContext != null
                && umbracoContext.HttpContext.Request != null;
            var request = validRequest ? umbracoContext.HttpContext.Request : null;
            var lang = validRequest ? request.QueryString["lang"] : "en-us";
            if (string.IsNullOrWhiteSpace(lang))
            {
                lang = "en-us";
            }
            var baseUri = default(Uri);
            var validBase = false;
            try
            {
                baseUri = new Uri(url);
                validBase = true;
            }
            catch
            {
                baseUri = new Uri("http://www.site.com/");
            }
            var builder = new UriBuilder(new Uri(baseUri, url));
            var path = builder.Path.TrimStart("/".ToCharArray());
            var langPart = lang + (string.IsNullOrWhiteSpace(path) ? null : "/");
            builder.Path = "/" + langPart + path;
            url = validBase ? builder.Uri.AbsoluteUri : builder.Uri.PathAndQuery;
        }
        catch (Exception ex)
        {
            LogHelper.Error<InternationalUrlProvider>(ErrorBuildingUrl, ex);
        }


        // Return URL.
        return url;

    }

    #endregion

}

And here's how I register that URL provider:

// Namespaces.
using Routing;
using Umbraco.Core;
using Umbraco.Web.Routing;


/// <summary>
/// Handles application startup.
/// </summary>
public class MyAppStart : ApplicationEventHandler
{

    #region Methods

    /// <summary>
    /// Application starting.
    /// </summary>
    protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication,
        ApplicationContext applicationContext)
    {

        // URL provider for international URL's.
        UrlProviderResolver.Current.RemoveType<DefaultUrlProvider>();
        UrlProviderResolver.Current.InsertType<InternationalUrlProvider>();


        // Boilerplate.
        base.ApplicationStarting(umbracoApplication, applicationContext);

    }

    #endregion

}

As I mentioned, I'm not yet using a content finder, so this is what my URL rewrites look like:

<?xml version="1.0" encoding="utf-8"?>
<urlrewritingnet xmlns="http://www.urlrewriting.net/schemas/config/2006/07">
  <rewrites>

    <!-- Rewrite international URL's. -->
    <add
      name="Localize URL (With QS)" rewriteUrlParameter="IncludeQueryStringForRewrite" ignoreCase="true"
      virtualUrl="^~/(?&lt;culture&gt;[a-z]{2}-[a-z]{2})(?&lt;url&gt;/((?!\?).)+\?.*|/?\?.*)$"
      destinationUrl="~${url}&amp;lang=${culture}" />
    <add
      name="Localize URL (No QS)" rewriteUrlParameter="IncludeQueryStringForRewrite" ignoreCase="true"
      virtualUrl="^~/(?&lt;culture&gt;[a-z]{2}-[a-z]{2})(?&lt;url&gt;/((?!\?).)+|)$"
      destinationUrl="~${url}?lang=${culture}" />

  </rewrites>
</urlrewritingnet>

That's a pretty good idea!

When I was using Umbraco myself, I was doing it this way: http://dimitros.be/en/blog/betterseowithpolyglot/

is working on a reply...