public function setLanguageId( $id )
	{
		if ( $id === $this->getLanguageId() ) { return; }

		if ( $id !== null ) {
			if ( strlen($id) !== 2 || ctype_alpha($id) === false ) {
				throw new MShop_Product_Exception(sprintf('Invalid characters in ISO language code "%1$s"', $id));
			}

			$id = (string) $id;
		}

		$this->_values['langid'] = $id;
		$this->setModified();
	}