>I think Greek is ranked with Russian because for both languages you require a different alphabet which means that it takes a long time to get off first base.<

Which brings us to the difference between learning to speak a language and learning to write a language. The two may have very different degrees of difficulty.

I remember watching rural Chinese children go through a set of character flashcards, sorting them into the ones they had studied and the ones they hadn't. They'd have failed a Chinese test, not because they couldn't speak Chinese, but because they were illiterate. Or only partially literate, to be more accurate.

I note that Japanese and Chinese both appear in the CIA's 'most difficult' list, and I suspect this is because they are testing language literacy as much if not more than language fluency.

BTW I once knew someone who was fluently illiterate in three languages!