Windows XP Home and Professional editions are released in 24 languages:
English, German, Japanese, Chinese (Traditional), Chinese (Simplified), Korean, Arabic, Hebrew, Spanish, French, Italian, Swedish, Dutch, Brazilian, Norwegian, Danish, Finnish, Czech, Polish, Hungarian, Russian, Portuguese, Greek, and Turkish.
Windows XP also offers more localized user interface languages via the Mulitilingual User Interface (MUI) Pack. See Windows XP & Windows 2000 MUI FAQ for details.
As in Windows 2000, the language and locale support offered in Windows XP is identical in each of the language versions. Whether you're using the English version or the Arabic version, you'll find you can still input, process and display text in Greek, Japanese, Korean or any of the other languages supported in Windows XP.