This plug-in is a "Full Jalali (خورشیدی - شمسی) Date and Persian (Farsi) (فارسی)" Support Package for wordpress by WP-Persian.com. This plug-in with listed features is a great tool for Iranian users of Wordpress.

• Full posts' and comments' dates' conversion.
• Jalali (Monthly and Daily) Archive template tag.
• Magic (Jalali/Gregorian) Calendar template tag.
• Jalali/Gregorian compatible permalinks.
• TinyMCE (Wordpress Editor) Persian improvements.
• Auto conversion of Arabic (ي , ك) to Farsi (ی , ک) with smart search
• Cross browser Persian keyboard support for themes' comment forms.
• Jalali Archive/Calendar fully customized widgets.
• Auto Persian numbers conversion.
• Fully customizable through specific Wordpress admin page.
• Jalali timestamp edit in new post and new page sections
• Jalali dates in edit tables
• Iran and Afghanistan month names.

This plug-in is now part of Persian Wordpress Project

1. 

   Persian Wordpress Admin Page

1. Extract the downloaded archive into wp-jalali folder. If you downloaded the .zip archive it contains the wp-jalali folder.
2. Upload wp-jalali to the /wp-content/plugins/ directory of your wordpress installation.
3. If you are using older versions of this plug-in, you must deactivate it first through the 'Plugins' menu in Wordpress admin.
4. Activate the plug-in through the 'Plugins' menu in Wordpress admin.

Where can I find more information and documentation about the plug-in?

You can read complete documentations on the plug-in documentation page in Persian (فارسی).

What is Wordpress Persian Project (پروژه وردپرس فارسی)

Just take a look at this page.