Apple released the tech specs for its new iPad on January 27, and they indicate its language capabilities are somewhat less that those of the iPhone and iPod Touch:
Language support for English, French, German, Japanese, Dutch, Italian, Spanish, Simplified Chinese, Russian
Keyboard support for English (US), English (UK), French (France, Canada), German, Japanese (QWERTY), Dutch, Flemish, Spanish, Italian, Simplified Chinese (Handwriting and Pinyin), Russian
Dictionary support for English (US), English (UK), French, French (Canadian), French (Swiss), German, Japanese, Dutch, Flemish, Spanish, Italian, Simplified Chinese (Handwriting, Pinyin), Russian
Whether the web browser and other apps might correctly display additional languages is unknown at this time. A test page for various scripts can be found here.
2/12 This page indicates iPad has browser support for Arabic display.
3/12 The Apple iPad Accessibility page say "VoiceOver speaks 21 languages and works with all of the applications built into iPad." This conforms with what is provided with some models of the iPhone and iPod Touch (and much superior to OS X, which is English only unless you buy 3rd-party voices). The list of languages is probably that found on this page.
The first iPads are supposed to be available April 3.