mysql function returns '??????' instead of correct string stored in table

Question

I have following situation:

CREATE TABLE `city` (
  `City_ID` int(11) NOT NULL,
  `CityName` varchar(20) NOT NULL,
  `Nomer` smallint(6) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

INSERT INTO `city` (`City_ID`, `CityName`, `Nomer`) VALUES
(7, 'Берлин', NULL),
(2, 'Васюки', NULL),
(3, 'Челябинск', NULL),
(4, 'Магадан', NULL),
(5, 'Екатеринбург', NULL),
(209, 'Чебоксары', NULL),
(455, 'Санкт-Петербург', NULL),
(6, 'Москва', NULL),
(458, 'Sochi', NULL),
(8, 'Париж', NULL),
(9, 'Бонн', NULL),
(10, 'London', NULL);

drop function if exists WhatIsCityName;
delimiter $$

create function WhatIsCityName(id int)
returns varchar(20)
begin
select cityname into @cityname from city where city_id=id;
return @cityname;
END $$

delimiter ;
select WhatIsCityName(7);

Last select returns '??????' instead of 'Берлин', though select WhatIsCityName(); returns correct value 'Moscow'