What factors make PHP Unicode-incompatible?

Question

I am able use UTF-8 characters just fine in my scripts.

As a matter of fact it is possible to have names of variables and functions contain Unicode characters.

Answer 1

Many of the string functions are just thin wrappers around C library equivalents, which also treat everything as a sequence of bytes. Another reason is that PHP carries around a lot of needless backward-compatibility baggage and thus gets stuck with bad design decisions from 3&4.

Maybe with 5.3's namespaces they'll finally have a way of phasing the old functions out.