Dominik Schwind

Adds a language taxonomy to posts, pages and other items.
This will add a URL scheme (Your Blog)/lang/(slug).
There is also a template tag for usage within the loop.
Example:
<pre><code><?php if(function_exists('lt_the_language')): ?>
<?php lt_the_language($post_id); ?>
<?php endif; ?>
</code></pre>

Language Taxonomy

Adds a language taxonomy to posts, pages and other items.

Louy Alakkad

This plugin gives you the ability to run the site in a language (Arabic for example) and use the admin panel in another (like English).
Just go to Settings » General and choose your language.

Admin Locale

This plugin allows you to change the language of the admin panel without changing the whole site language.

Language Taxonomy vs Admin Locale