which is the world's most difficult language?

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It's pretty hard to say what the world's most difficult language is. For an English speaker, it wouldn't be Icelandic -- that's a Germanic language (as is English), and while it is apparently quite hard to learn, the basic grammar is likely somewhat similar. For an English speaker, the most difficult languages to learn would be ones that aren't Indo-European languages; Mandarin or Japanese or some other east Asian language would probably be the most confusing for an English speaker.

Indo-Aryan is a language sub-family that's present in the Indian subcontinent. Indo-Aryan is part of a much larger group of languages called Indo-European. That family includes Hindi, Farsi, Greek, English, Russian, Spanish, Icelandic and many other languages. Indo-European has many sub-families, like the Germanic branch, the Slavic branch, and the Romance branch (these groups compose the majority of languages spoken in Europe). Really, just check out the wikipedia page for a basic understanding.

How did they come into being? Uh, I'll leave that one for someone else...

Why the rolling eyes?