I'm not 100% sure on this, but I think multilanguage just means you can install various languages on the device and read pages that render those language fonts, and the east asia OS's mean you can actually type input in those languages. At least, for Japanese, I know this to be true.
Jonneh is correct. Multilanguage covers mainly languages from Europe and the middle east whereas East Asia covers Asians languages such as Korean, Chinese, Thai, & Japanese (this includes input as well). Although the East Asia version is geared toward users who need Asian language input support, it does include some European languages such as English UK, French, German, Italian, etc.
