The hardest language to learn is the one you have the least motivation to learn. The "easiest" language to learn is the one you have the most motivation to learn. Also, no language is really any harder or easier to learn than another, if by "learn" you mean to reach an intermediate or advanced level--say by the time you start reading the literature. Many people in the USA consider Spanish an easy language to learn, and something like German "a lot harder." But after the first two years of any language, they all have about the same difficulty level, in my experience. But it is true that if you learn a language that is somehow related to yours, either it's in the same language family, or it has a lot of borrowed words, then that might be easier to /start/ learning than a language that works a lot differently than yours does.

There is one language that is easier than others (Esperanto), but that is because is a planned language which was specifically created to be simple and completely regular... Apart from that, all languages have difficult features and simple ones, also, to get to a fluent/conversational level, it doesn't matter how many words the whole language has (I don't think a native Arabic speaker knows more words in Arabic than a native French speaker knows in French).

But you don't need to know all those words to speak the language fluently, Emir.