character length of varchar values are calculated incorrectly for some characters

[jennifersp]

character length of San Pedro de Macorís = 20, but len() function returns 21 as len("í") = 2

CREATE TABLE `city` (
  `ID` int NOT NULL AUTO_INCREMENT,
  `Name` char(35) NOT NULL DEFAULT '',
  `CountryCode` char(3) NOT NULL DEFAULT '',
  `District` char(20) NOT NULL DEFAULT '',
  `Population` int NOT NULL DEFAULT '0',
  PRIMARY KEY (`ID`)
);

INSERT INTO `city` VALUES (1,'San Pedro de Macorís','DOM','San Pedro de Macorís',124735);

error message : string is too large for column