English is not "sloppy", not any more than any other language. Any language with a large number and geographic spread of speakers will develop varieties and accents. In fact people do it deliberately to distinguish themselves from other speakers of the same language (just take a look at how teenagers' language innovates). French, Spanish, and German all have huge variation in dialects and accents too.
English, like many other languages learnt widely as a trade language by non-native speakers, has lost a lot of complexity, notably case system and gender. (Indonesian is perhaps the canonical example of this.) Unfortunately its spelling was standardized just before it underwent a huge change in pronunciation, and its habit of borrowing words from other languages without changing their spelling, has left it with fairly chaotic orthography. A few phonetic features - unusual consonants like th, difficult to learn rules around stressed syllables, nasty consonant clusters (squirrel!) - do make it tricker than it could be for second language learners.
It didn't become the default international language of trade due to any features of the language itself (it did that thanks to the British Empire and in particular its former colony in North America) - but many features of modern English are the result of so many people learning and speaking it.
Because it is so widely spoken by so many people, it does have a large vocabulary and a lot of idioms. But the grammar is generally not too difficult - no grammatical gender, no case aside from a few pronouns, outside of a handful of irregular verbs conjugations are pretty easy ("put an 's' on the third person singular"), and so on.