This deprecated CharAt and CharCodeAt for being unsuitable for text processing and in the case of CharCodeAt also for being buggy.
A new replacement, ByteAt has been added that reads a string byte by byte, as well as CodePointCount, which counts the amount of Unicode code points in a string and GetNextCodePoint which reads the string code point by code point.
Note that while this woll work as intended with the currently supported languages as a means to read single characters, there is no guarantee that this will remain so if Unicode support gets extended to things which break the "one code point == one character" assumption.