In C and C++, the source character set is implementation defined. This means that each compiler sets its own rules about what characters are accepted. For example compilers could choose to accept ASCII or EBCDIC or Unicode, or some combination, etc.

So the ISO standard will say that ; character is the end of statement punctuation. But it is up to the compiler to say which character(s) or code point(s) represent the ISO ;.

The ISO standards also require compilers to define a separate execution character set to specify values that can be stored in char and used with the string library functions. The execution character set doesn't have to be the same as the source character set.

Edit: I should also mention that the rules for this stuff are changing a lot in ISO C23 and C++23. (Which standards I haven't yet personally adopted.) Basically the ISO 23 standards mandate compilers to support UTF-8 source files, and they map every source character in the ISO standard to its corresponding Unicode character.