Python2 supports Unicode, but it requires careful thought and deliberation to do it right - and at the same time makes it very easy to do it wrong (by assuming all bytes are strings etc). As a result, when such code is written by people with little awareness of the world beyond ASCII or Latin-1, it tends to be buggy with locales that need more than that.

And yes, it's not really a Python issue, it's a more generic issue with treating bytearrays as strings (what you refer to as POSIX text model). Until UTF-8 became the standard encoding everywhere, there were many Linux apps that couldn't handle non-Latin1 encodings properly, either. It was also the case on Windows in 9x days, for all the same reasons.