A MUI installs another language for your windows installation, meaning if you have an English version you can change the language to one of the following languages.

The ISO contains the following languages.

0401 Arabic                 ARA.MUI
0402 Bulgarian                 BG.MUI
041a Croatian                 HR.MUI
0405 Czech                 CS.MUI
0406 Danish                 da.MUI
0413 Dutch (Standard)         NL.MUI
0425 Estonian                 ET.MUI
040b Finnish                 FI.MUI
040c French (Standard)         FR.MUI
0407 German                 GER.MUI
0408 Greek                 EL.MUI
040d Hebrew                 HEB.MUI
040e Hungarian                 hu.MUI
0410 Italian                 IT.MUI
0411 Japanese                 JPN.MUI
0412 Korean                 KOR.MUI
0426 Latvian                 LV.MUI
0427 Lithuanian                         LT.MUI
0414 Norwegian                 no.MUI
0415 Polish                 pl.MUI
0416 Portuguese (Brazil)         Br.MUI
0816 Portuguese (Standard)   PT.MUI
0418 Romanian                 RO.MUI
0419 Russian                 RU.MUI
0804 Simplified Chinese          CHS.MUI
0c0a Spanish (Modern Sort)    ES.MUI
041b Slovak                 SK.MUI
0424 Slovenian                 SL.MUI
041d Swedish                 SV.MUI
041e Thai                 TH.MUI
0404 Traditional Chinese        CHH.MUI
041f Turkish                 TR.MUI

Just mount the MUI.ISO file in [insert your mounting tool] or burn it with your [insert your favorite burning software].

No key needed.
Download
/Files/CN/Multi_Language_Installer_For_windows_XP.zip