Index: wp-includes/locale.php
===================================================================
--- wp-includes/locale.php	(revision 19832)
+++ wp-includes/locale.php	(working copy)
@@ -85,16 +85,6 @@
 	var $text_direction = 'ltr';
 
 	/**
-	 * Locales which are known to be right-to-left.
-	 *
-	 * @since 3.4.0
-	 * @var array
-	 * @access private
-	 * @static
-	 */
-	private static $rtl_locales = array( 'ar', 'ckb', 'fa_IR', 'he_IL', 'ug_CN', 'dv', 'fa_AF', 'ha', 'ps', 'uz_UZ', 'yi' );
-
-	/**
 	 * Sets up the translated strings and object properties.
 	 *
 	 * The method creates the translatable strings for various
@@ -190,7 +180,7 @@
 		// Set text direction.
 		if ( isset( $GLOBALS['text_direction'] ) )
 			$this->text_direction = $GLOBALS['text_direction'];
-		elseif ( is_textdomain_loaded( 'default' ) && self::is_locale_rtl( get_locale() ) )
+		elseif ( 'rtl' == _x( 'ltr', 'text direction' ) )
 			$this->text_direction = 'rtl';
 	}
 
@@ -336,19 +326,6 @@
 	function is_rtl() {
 		return 'rtl' == $this->text_direction;
 	}
-
-	/**
-	 * Determines whether a locale is known to be right-to-left.
-	 *
-	 * @since 3.4.0
-	 * @static
-	 *
-	 * @param string Locale in WP format.
-	 * @return bool Whether locale is RTL.
-	 */
-	public static function is_locale_rtl( $locale ) {
-		return in_array( $locale, self::$rtl_locales );
-	}
 }
 
 /**
Index: wp-includes/load.php
===================================================================
--- wp-includes/load.php	(revision 19832)
+++ wp-includes/load.php	(working copy)
@@ -726,8 +726,6 @@
 					load_textdomain( 'default', $location . '/' . $locale . '.mo' );
 					if ( defined( 'WP_SETUP_CONFIG' ) && file_exists( $location . '/admin-' . $locale . '.mo' ) )
 						load_textdomain( 'default', $location . '/admin-' . $locale . '.mo' );
-					if ( WP_Locale::is_locale_rtl( $locale ) )
-						$text_direction = 'rtl';
 					break 2;
 				}
 			}