English is a complicated language to learn..even then its the universal language-why?

I find your questions really interesting.  I think all all languages are complex.   Think of all the things we need to say including sometimes subtle nuances of meaning and humour.  In all natural languages it is possible to express such a wide range of meanings.  If a language was very simple, would we be able to do all this? And would it be a very interesting language?

But, is English more difficult than other languages?  I would say that difficulty depends on the distance between your  own first language and the language you are trying to learn.  I find Spanish quite easy because there are some similarities with English.  But If I tried to learn an Asian language I would really find it tough.

However, your questions seems to be asking why a complicated language has become the universal language.  It wasn't chosen because it was easy to learn but because of the way things have developed politically i.e. the importance of the US as world superpower.

I'd love to know what you think

I don't think English is very complicated language. As far as I know, there is more troubles when you're learning Russian, for example. :)

"there are more troubles", of course :) shame on me :)

As far as I can see, latin-derived languages like portuguese and spanish are far more complicated than English.
See German (as a non latin language). Everyone I ever heard talking about learning a language tought german was.. absurdelly hard. While english.. wasn't.

Possibly basic English is not very difficult. First of all, it lost a  lot of inflections in the course of its history. Hence, you needn't learn declensions and conjugations.
But if you want to achieve a very high level of knowledge, it will take years and years, your whole life. English is the language (it is a fact proved by linguists) which possesses the greatest vocabulary compared with other languages (I mean the number of lexical items - the corpus of its wordstock). New words and phrases emerge daily. Also there are such phenomena as extensive polysemy, idioms, phrasal verbs.
It is an international language, of course, because of the role the U.S.A. plays in modern life. I would recommend a wonderful book - Cambridge Encyclopedia of the English Language by D.Crystal.

 Some of these answers do not look at the historical reasons. English is popular because of Microsoft Windows?! No, it has more to do with the spread of the British Empire around the world in centuries past. Look at a list of the countries Britain colonised and you see how the language got a toe-hold all over the globe. English's only real rival was French. If the French had won the battles for North America then peut-être French would now be the world's lingua franca, as it would have been the language of choice in North America. Hard to imagine, but if wasn't for the outcomes of battles in the eighteenth century, Rambo would have been speaking French!