There isn't one. Unless you're using a fixed-width font character placement doesn't equal the human placement (length); and if you're limited by technical mean

There isn't one. Unless you're using a fixed-width font character placement doesn't equal the human placement (length); and if you're limited by technical means you usually care about the raw encoding (byte/octets?) length of the underlying encoding. In both cases, for anyone that cares about the limit, the starting byte / octet for the next character is probably sufficient knowledge and offset, and update that accordingly with some movement iterations jumping multiple units if the traversed element is wide.