The way you coded it, with numeric character references, will always work in HTML, no matter what the "charset" is. Those strings will not be interpreted as Unicode within Perl or pretty much anywhere else that you write them. (An XML processor will interpret them as a web browser would.)

If you want to code the strings so that they can be used generally, you need to replace

 'Κυ'
with
 "\x{39A}\x{3C5}"
[download]

and to use utf8; How these strings are used elsewhere is still complicated