Phrase

This plugin allows you to send page or post content to your Phrase projects, directly from within WordPress. Once translations are done, send them back to WordPress and easily publish multilingual sites.

Phrase Strings

Phrase WordPress Integration. Phrase is a translation management platform for software projects. You can collaborate on language file translation with …

Oleg Butuzov

For WP 2.3 – 2.5 you should user 1.3.* version
WP_Multilingual is extension that brings WordPress multilingual support. With it’s help you can publish more that in one language at a time. Its easy, cheap and simple way to use multilingual advantages of blogging.
With this plugin you can manage your Posts/Pages/Categories/Blogroll Links/Tags in multilingual mode.
Plugin also allow you to localize theme relate to Selected language, and localize Wp-admin in your language. 
Plugin Localized in
<ul>
<li>Russian</li>
<li>Ukrainian</li>
<li>English</li>
<li>Franch</li>
<li>Italian</li>
<li>Greek</li>
<li>Spanish</li>
<li>Czech</li>
<li>Catalan</li>
<li>Herbew</li>
<li>Deutsch</li>
<li>Dutch (Holland or Netherlands)</li>
<li>Arabian</li>
<li>Polish</li>
</ul>

WP_Multilingual

WP_Multilingual is extension that brings WordPress multilingual support. With it's help you can publish more that in one language at a time.

Phrase Strings vs WP_Multilingual