If you can write your posts in 2 or more(Woo…) languages within one blog, you might want to tell the client browser the language attribute of you posts.
According to <a href="http://www.w3.org/International/tutorials/language-decl/en/all.html" title=" W3C tutorial" rel="nofollow ugc">the tutorial on W3C</a>, language attribute can be declared in the container html tag of your post like this: 
<div id=”post_id” class=”post_entry” lang=”zh-Hant” xml:lang=”zh-Hant” dir=”ttb”>… 
Here “zh-Hans” is the language attribute of your post which means it’s written in Simplified Chinese.
This plugin gives your post a language tag by adding a meta deta to that post.
To add language tag, select it from the language box when you compose/edit a post. Select “None” will delete the language tag.
<h3>Revisions</h3>
2007-12-18, 
0.2: Now you can difine language direction. 
 Insert CSS style into page head automatically to support pretty printing.
 readme file updated for new feature and fixed a error
2007-07-23 
0.1: First release

Multilingual post

This plugin adds a standard compliant language tag to your post and page.

dileep1984

A wordpress plugin which provide a powerful functionality to type post or page description in your selected language into wordpress site/blog. 
In this plugin user can select language and then type word in english after space it will convert word into selected language. This plugin uses Google transliteration api.

Typing Language

useful for typing in any language

WordPress Plugin Typing language for type post or page description in your selected language.

Multilingual post vs Typing Language