...
It is perfectly fine for scopes that are not visible to each other to have duplicate identifiers. For instance, two functions may each have a local variable with the same name, as their scopes can not cannot access each other. But a function's local variable names should be distinct from each other, as well as from all static variables declared within the function's file (as well as all included header files.)
...
Restriction of the significance of an external name to fewer than 255 characters in the standard (considering each universal character name or extended source character as a single character) is an obsolescent feature that is a concession to existing implementations. As a result, it is not necessary to comply with this restriction , as long as the identifiers are unique and the assumptions concerning the number of significant characters are documented.
...