Note that iso-8859-1 is a unicode encoding -- it just doesn't support all of the characters.
I don't know what you mean by "unicode encoding" (are there encodings that map to non-unicode chars?), but in the perl context it's worth mentioning that iso-8859-1 strings don't follow unicode-semantics by default, the need to be encoded like any other string:
# this file is stored as latin1
print "ä" =~ m/\w/ ? "Unicode\n" : "Bytes\n";
Perl's unicode support is great, but the programmer MUST learn the difference between unicode and utf-8, and the difference between text data and binary data.
Yes, and they have to learn that for any kind of tool that supports Unicode and different encodings.
And I really like the Perl 6 spec which allows string operations on byte, codepoint and grapheme level ;-)