What is the best place to display the language in your URL?

I have a multi-language website that makes use of pretty URLs, so called search-engine-friendly URLs.

Now there are a few places to define the language in the URL:

1. • www.example.com/en/articles/random
   • www.example.com/nl/articles/random
2. • en.example.com/articles/random
   • nl.example.com/articles/random
3. • www.example.com/articles/random?lang=en
   • www.example.com/articles/random?lang=nl

Is there any preferred way of showing this, or is there another better way that I did not include?

I have found a nice resource from Google on the choices you can make. There is a section with pros and cons of each method you can use.

I have been struggling with the multi-lingual websites for a while now.

There are definitely some points in the article that are not mentioned in the answers mentioned. That why I felt the need to post this as an answer. I hope this helps someone out.