If you want to reach an international audience, you must make sure that there is an option of translation in your blog. We all know how inconvenient it is to come across something of interest in an unknown language. Copying and pasting the content in a translator to get it translated ruins the very idea of searching through web. I have put together a list of plugins that can help you with translation for your WordPress blog.
Google AJAX Translation
Add Google AJAX Translation to your blog. This plugin allows your readers to translate your blog posts, pages, or comments into 52 languages.
Transposh WordPress Translation
Transposh translation filter for WordPress offers a unique approach to blog translation. It allows your blog to combine automatic translation with human translation aided by your users with an easy to use in-context interface.
Global Translator
Automatically translates your blog in 48 different languages!
Codestyling Localization
You can manage and edit all gettext translation files (.po/.mo) directly out of your WordPress Admin Center without any need of an external editor. It automatically detects the gettext ready components like WordPress itself or any Plugin / Theme supporting gettext, is able to scan the related source files and assists you using Google translate API during translation. This plugin supports WordPress MU and allows explicit WPMU Plugin translation too. It newly introduces ignore-case and regular expression search during translation. BuddyPress and bbPress as part of BuddyPress can be translated too. Produces transalation files are 100% compatible to PoEdit.
gtrans
Make your website available to the world using Google Translate.
qTranslate
Adds userfriendly multilingual content management and translation support into WordPress.