Index: units/helpers/multilanguage_helper.php
===================================================================
--- units/helpers/multilanguage_helper.php	(revision 14103)
+++ units/helpers/multilanguage_helper.php	(working copy)
@@ -193,6 +193,35 @@
 			}
 		}
 
+		/**
+		 * Creates missing multilanguage fields in table by specified prefix
+		 *
+		 * @param string $prefix
+		 * @param int $src_language
+		 * @param int $dst_language
+		 */
+		function copyMissingData($prefix, $src_language, $dst_language)
+		{
+			$table_name = $this->Application->getUnitOption($prefix, 'TableName');
+			$this->curFields = $this->Application->getUnitOption($prefix, 'Fields');
+
+			if (!($table_name && $this->curFields) || ($table_name && !$this->Conn->TableFound($table_name))) {
+				// invalid config found or prefix not found
+				return true;
+			}
+
+			foreach ($this->curFields as $field_name => $field_options) {
+				$formatter = isset($field_options['formatter']) ? $field_options['formatter'] : '';
+
+				if ( ($formatter == 'kMultiLanguage') && !isset($field_options['master_field']) ) {
+					$sql = 'UPDATE ' . $table_name . '
+							SET l' . $dst_language . '_' . $field_name . ' = l' . $src_language . '_' . $field_name . '
+							WHERE l' . $dst_language . '_' . $field_name . ' = "" OR l' . $dst_language . '_' . $field_name . ' IS NULL';
+					$this->Conn->Query($sql);
+				}
+			}
+		}
+
 		function deleteField($prefix, $custom_id)
 		{
 			$table_name = $this->Application->getUnitOption($prefix, 'TableName');
Index: units/languages/languages_config.php
===================================================================
--- units/languages/languages_config.php	(revision 14103)
+++ units/languages/languages_config.php	(working copy)
@@ -28,16 +28,6 @@
 			'Conditional' => false,
 			'HookToPrefix' => 'lang',
 			'HookToSpecial' => '*',
-			'HookToEvent' => Array ('OnSave'),
-			'DoPrefix' => '',
-			'DoSpecial' => '',
-			'DoEvent' => 'OnUpdatePrimary',
-		),
-		Array (
-			'Mode' => hAFTER,
-			'Conditional' => false,
-			'HookToPrefix' => 'lang',
-			'HookToSpecial' => '*',
 			'HookToEvent' => Array('OnSave', 'OnMassDelete'),
 			'DoPrefix' => '',
 			'DoSpecial' => '',
Index: units/languages/languages_event_handler.php
===================================================================
--- units/languages/languages_event_handler.php	(revision 14103)
+++ units/languages/languages_event_handler.php	(working copy)
@@ -104,7 +104,7 @@
 				/* @var $object LanguagesItem */
 
 				$object->Load($id);
-				$object->setPrimary();
+				$object->copyMissingData( $object->setPrimary() );
 			}
 		}
 
@@ -129,7 +129,7 @@
 			foreach ($ids as $id) {
 				$object->Load($id);
 				if ($object->GetDBField('PrimaryLang')) {
-					$object->setPrimary(true, false);
+					$object->copyMissingData( $object->setPrimary(true, false) );
 				}
 
 				if ($object->GetDBField('AdminInterfaceLang')) {
@@ -310,6 +310,7 @@
 			$this->Application->RemoveVar($var_name);
 
 			$event->CallSubEvent('OnReflectMultiLingualFields');
+			$event->CallSubEvent('OnUpdatePrimary');
 		}
 
 		/**
Index: units/languages/languages_item.php
===================================================================
--- units/languages/languages_item.php	(revision 14103)
+++ units/languages/languages_item.php	(working copy)
@@ -22,10 +22,24 @@
 			return $this->Conn->GetOne($sql) + 1;
 		}
 
+		/**
+		 * Set's current language as new primary and return previous primary language
+		 *
+		 * @param bool $reset_primary
+		 * @param bool $admin_language
+		 * @return int
+		 */
 		function setPrimary($reset_primary = true, $admin_language = false)
 		{
+			$prev_primary = false;
 			$primary_field = $admin_language ? 'AdminInterfaceLang' : 'PrimaryLang';
+
 			if ($reset_primary) {
+				$sql = 'SELECT ' . $this->IDField . '
+						FROM ' . $this->TableName . '
+						WHERE ' . $primary_field . ' = 1';
+				$prev_primary = $this->Conn->GetOne($sql);
+
 				$sql = 'UPDATE '.$this->TableName.'
 						SET '.$primary_field.' = 0';
 				$this->Conn->Query($sql);
@@ -39,9 +53,34 @@
 			// in case, when Update method is called for this langauge object
 			$this->SetDBField($primary_field, 1);
 			$this->SetDBField('Enabled', 1);
+
+			return $prev_primary;
 		}
 
 		/**
+		 * Copies missing data on current language from given language
+		 *
+		 * @param int $from_language
+		 */
+		function copyMissingData($from_language)
+		{
+			if ( !is_numeric($from_language) || ($from_language == $this->GetID()) ) {
+				// invalid or same language
+				return ;
+			}
+
+			$ml_helper =& $this->Application->recallObject('kMultiLanguageHelper');
+			/* @var $ml_helper kMultiLanguageHelper */
+
+			$to_language = $this->GetID();
+			$this->Application->UnitConfigReader->ReReadConfigs();
+
+			foreach ($this->Application->UnitConfigReader->configData as $prefix => $config_data) {
+				$ml_helper->copyMissingData($prefix, $from_language, $to_language);
+			}
+		}
+
+		/**
 		 * Allows to format number according to regional settings
 		 *
 		 * @param float $number