Your native language is the easiest and languages with other way of writing and speaking are the hardest. I personally think that Filipinos find it easier to learn English since Filipino and English has the same set of alphabet. Even I'm interested at it, I find it very difficult to learn Arabic.

It depends on what your mother language is. If you look at this link http://www.biblical-data.org/OCS/IE_tree.jpg you see that a lot of languages have the same language history. They are all evolved from indo-european languages. If you look at Chinese of Japanese its different. Because they do not come from indo-european languages. (Japanese and Chinese also have no common language ancestor(The Japanese only stole the Chinese characters for there kanji system)). So for me as a Dutchman learning English is way more easy then learning Japanese! So the answer to this question is different for every person. Its about your mother language, the language you want to learn. And how much they have in common. And that again depends on the history of the languages. Generally saying, they say that Chinese is the hardest language to learn, because it has the most characters to learn.(around 6000-12000 or even more)