The Economist has an article about how languages can be said to be, comparatively speaking, more or less complex. The grand prize for most complex language goes to one in the Amazon:
Link via Marginal Revolution | Image: NASA
With all that in mind, which is the hardest language? On balance The Economist would go for Tuyuca, of the eastern Amazon. It has a sound system with simple consonants and a few nasal vowels, so is not as hard to speak as Ubykh or !Xóõ. Like Turkish, it is heavily agglutinating, so that one word, hóabãsiriga means “I do not know how to write.” Like Kwaio, it has two words for “we”, inclusive and exclusive. The noun classes (genders) in Tuyuca’s language family (including close relatives) have been estimated at between 50 and 140. Some are rare, such as “bark that does not cling closely to a tree”, which can be extended to things such as baggy trousers, or wet plywood that has begun to peel apart.
Most fascinating is a feature that would make any journalist tremble. Tuyuca requires verb-endings on statements to show how the speaker knows something. Diga ape-wi means that “the boy played soccer (I know because I saw him)”, while diga ape-hiyi means “the boy played soccer (I assume)”. English can provide such information, but for Tuyuca that is an obligatory ending on the verb. Evidential languages force speakers to think hard about how they learned what they say they know.
Link via Marginal Revolution | Image: NASA
English grammar can be picked up with speaking.
not exactly the case in Arabic.
English is messy, but not difficult. Yes, its phonetics is complex, but French, for example, is not really straightforward, too. English grammar is quite simple, compared to German, French (again) or Scandinavian languages.
The only real issue is vocabulary: English vocabulary is extremely rich and comes from very different origins, which makes "structured" learning difficult (i.e. etymology is complex). However, if you stick to basic, everyday vocabulary, it's easy, and moreover, you just have to know a few common phrasal verbs (what you call "compounds words").
Some languages are easier to learn than others, because of shared origins. For example, Italian, Spanish, Portuguese and French are Romance languages. If you speak one, learning another one is easy. You can even decipher a (not too complex) written text without having learned the language.
For somebody speaking a really different language (Asian, for instance), English is not more difficult to learn than other common European languages.
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English?