Перевод - Японский-Английский - この世界は、 不穏です。

I think the best way to translate "fuon" is "threatening".

Really? Well, maybe you´re right. Actually, my problem is that there are so many meanings of that word and they can fit this sentence. Is unfair a very rarely used meaning of this word? Because I´ve looked it up in several dictionaries, even asked my Jp teacher who said it can be OK so. I´ll look it up again, but actually I feel ´unfair´ sounds better and it´s even so true... :-P

I guess that if you displaid totality of the definitions from this Japanese word, it would suit as well, so, due to the lack of context, this translation is right.
Just adding the other adjectives in the comment area as other possible ways to translate "fuon" would be fine...

Merci bcp, Francky.