The latest version of the iBookstore Publisher User Guide, dated 1/19/12, has the same language exclusions as the one from 2010:
"What languages does the iBookstore NOT support?
At this time, the iBookstore does not support the following languages: Persian, Old (ca.600- 400 B.C.), Persian, Samaritan Aramaic, Amharic, Arabic, Official Aramaic (700-300 BCE), Imperial Aramaic (700-300 BCE), Burmese, Chinese, Hebrew, Japanese, Judeo-Persian, Judeo- Arabic,Central Khmer, Lao, and Mon-Khmer languages."
I wonder if this is really accurate. If readers find books in the store in Chinese, Japanese, Arabic, or Hebrew, I would welcome hearing about it.
PS I have personally found a lot of Chinese books in the store, so clearly that language is in fact supported.