I am not an expert and may be off-base here. But I believe that Chinese and Semitic writing systems are right-to-left (in the Chinese case, up-to-down first) and that these cultures used predominantly lunar calendars. Meanwhile, Western and Mayan writing systems are left-to-right, and these cultures used predominantly solar calendars. The moon waxes from right to left. Is it possible that calendar systems influenced writing direction?
The Persian calendar is a solar calendar. Persian is a right-to-left language. (Both the older Pahlevi form and the modern Arabic-derived one.)<p>The Chinese calendar is, technically speaking, a lunisolar calendar. The Hindu and Thai calendars are also lunisolar. Thai is right-to-left.<p>There does not appear to be a correlation.