TXT & RTF, no, PDF, yes -- you can put whatever you want in a PDF and it'll render it, with the qualification that you need to make the PDF pages the right size for the Reader's display. I don't think you could embed the a Chinese font into an LRF file using something like BookDesigner. I know that you can embed fonts in BD, but if I recall correctly it doesn't extend to radically non-English chars.
