When building a multi-lingual website (with ASP.NET web forms), I\'ll use an HTTP module to rewrite the URLs to end up with something friendly (for humans & search engin
You can do this, but keep in mind that not all countries are languages. For example, en-gb is the usual representation for British English, or more specifically, the Great Britain locale for English content, for example. If you can, it's worth following the RFC1766-derived conventions for language-LOCALE.
Search engines actually tend to do a fairly good job dealing with content-negotiation, by the way, so you need not necessarily have separate URIs for the same content in different languages. Google Japan will crawl with ja-JP as the accept language header, for example.