That webpage uses the charset Windows 1253 to encode it, it's similar to the greek charset (ISO/IEC 8859-7) so you must first encode those bytes/code point in utf8, but you must encode the characters corresponding to each byte/code point in the greek charset, not in unicode (there is no support for the Window 1253 codepage/charset as far as I know with $utfencode and $utfdecode):
Take a look
here for more information about it, but I'll explain a bit:
Takes the Gamma letter for example, it has the code point 195 in the greek charset, it has the code point 915 in unicode. In mIRC $chr(915) evaluate to that letter.
$utfencode($chr(915)) produces the utf8 sequence of the unicode code point used (915).
$utfencode($chr(195),161) produces the utf8 sequence of the character corresponding to the code point used (195) in the specified charset (161 being the greek charset).
So both are equivalent.
Now back to your example you know you're dealing with the greek charset (a similar charset in reality: windows 1253) so you are going to use $utfdecode($utfencode(TEXT,161)).
$utfencode(TEXT,161) will encode each byte (according to the greek charset, as we said) in utf8, and then $utfdecode will decode that back.
$utfdecode($utfencode(TEXT,1)) is just TEXT because 1 is the default.
