Fahad Alduraibi

Do you write posts in different languages that have different directions? 
This plugin enables a feature in the post editor which allow writing texts in Left-to-Right and Right-to-Left directions in the same post (or page) so you can write in English (and any other LTR language) and also RTL languages like Arabic, Persian and Hebrew.
Simply look for the new buttons added to the post editor after installing the plugin. (See the screenshots for better understanding)
اضافة زرارين لشريط التحرير لتمكين تحويل النص للقراءة من اليمين لليسار مثل اللغة العربية والفارسية والعبرية
<a href="http://www.fadvisor.net/blog/2008/10/wp-rtl/" rel="nofollow ugc">More details</a>
<ul>
<li>Note: This plugin will not change the direction of the post title, since that is controlled by the theme.</li>
</ul>

WP-RTL

Adds two buttons to the TinyMCE editor to enable writing text in Left to Right (LTR) and Right to Left (RTL) directions.

.fay

This plugin auto detects and apply the right direction (RTL or LTR) on post’s titles, bodies and comments.
According to WordPress, adding support for language written in a Right To Left (RTL) direction is just a matter of overwriting all the horizontal positioning attributes of your CSS stylesheet in a separate stylesheet file named rtl.css. 
But this solution is working only when you have just an RTL blog (or just an LTR blog using the classical style.css). 
One of solutions: We will let WordPress applying the same style.css to both of RTL/LTR posts and this plugin will automatically detect the post language to correct its direction.
It’s just a beta version that I tested with the WordPress default theme, please let me know your feedback with your own complexed css.

WP Direction Detector

This plugin auto dectects and apply the right direction (RTL or LTR) on post's titles, bodies and comments.

WP-RTL vs WP Direction Detector