Learning a language as an adult strongly depends on the learner's native language. Therefore it is meaningless to make a universal ranking of difficulty. For example, a native English speaker will learn Frisian - and vice versa - much more easily than a native Japanese speaker would. In general, the closer the second language is in relation to vocabulary, sounds, sentence structure, culture, and other factors to the learner's native tongue and culture, the easier acquisition will be. This "proximity" of the target language is not necessarily a function of genetic relationship but may also be polyphyletic, such as a chance similarity of phonology. English speakers often consider Spanish to be very easy to learn, for example, even though Spanish is not the closest relative of English. Differences in phonology are often insurmountable for the learner, and will be apparent in an accent in non-native speakers even after many years of proficient use of the learned language.
--------------------------------------------------------------------------- Man's enemies are not demons, but human beings like himself
Nature is not human hearted
Knowing others is intelligence; knowing yourself is true wisdom. Mastering others is strength; mastering yourself is true power
If taken literally, the hardest languages for outsiders to learn would be those that are currently unknown by outsiders, for example, Sentinelese. Sentinelese is completely unattested, and no Sentinelese have had significant contact with outsiders for several centuries, so it cannot be learned anywhere but on North Sentinel Island. However, it is illegal for anyone to visit the island, and fishermen accidentally visiting have been killed by the Sentinelese
--------------------------------------------------------------------------- Man's enemies are not demons, but human beings like himself
Nature is not human hearted
Knowing others is intelligence; knowing yourself is true wisdom. Mastering others is strength; mastering yourself is true power
Hebrew is easy, maybe I say that because it's close to Arabic, I heard Arabic is hard to learn for foreign people, I'd go with Japanese from that list.
Japanese isn't too terrible if you're dedicated. I know a few people who've successfully learnt it, including the characters.
I actually judged from characters and Animes. LOL
--------------------------------------------------------------------------- ~King of Dark~ ♮C.0.W♮ My Past has determined your future My torrential pain will be your unspeakable suffering Your days are numbered Don't fear the end Pray for it and unlike your own immortality My thirst for vengeance WILL NEVER DIE