How to activate RTL in wordpress twenty eleven
Do normal englsih installation
Download a copy of arabic wordpress.
Copy the file wp-content/languages/ar.php from arabic version to english version
Go to wp-config.php and add define(‘WPLANG’, ‘ar’);
Khalas, you get an Englsih wordpress in RTL
Then install Admin in English plugin.
To make frondend arabic and backend english continue with below steps
Add languages folder form arabic version to english version