Codepages in mIRC? Thats simple.
I used iconv (linux program) for create 125 codepages (6.4 MB)

Syntax (like in subject): $codepage(from,to,string)

Example: $codepage(cp1251,utf-8,$+($chr(242),$chr(229),$chr(241),$chr(242)))
Converts Cyrillic (codepage Windows-1251) word "теÑÑ‚" to utf-8 codepage.

Example alias:

alias cp_example {
  ; теÑÑ‚ (russian) = test (english)
  var %string = теÑÑ‚, %source = %string

  ; from UTF-8 to Windows-1251
  var %string = $codepage(utf-8,cp1251,%string)

  ; from Windows-1251 to KOI8-R
  var %string = $codepage(cp1251,koi8-r,%string)

  ; from KOI8-R to Windows-1251
  var %string = $codepage(koi8-r,cp1251,%string)

  ; from Windows-1251 to UTF-8
  var %string = $codepage(cp1251,utf-8,%string)

  ; Check
  echo -a Success, %source = %string yep? :)
}

Archive contains codepage.mrc - script/snippet, and codepage directory, with MORE codepages!
Enjoy. ;)