Language is never 'invented', it never has a definite starting point. Langaue evolves on a daily basis, and it adopts words and phrases from other languages, brought in from various visitors and invaders. hence, English has its roots in Latin, and various European languages. American speech is peppered by its variety of imported cultures, and so in fact is every spoken language in the word, with the posible exception of isolated tribes in the inaccessable areas of the world where no influx from outsiders has occured.
As Andy rightly states, no human language is invented - sounds simply change and evolve over the centuries, according to a thousand different cultural and linguistic influences - English as much as any. The compulsory text-book on this subject when I studied English at uni years ago was "The History of the English Language" by A.C. Baugh and Thomas Cable. Certainly not a lightweight read, but everything you could ever wish to know, from early Anglo-Saxon onwards.
It evolved about 1200 years ago from Latin, Anglo-Saxon, Jutish, French, Germanic, Norse etc.
The first two answers arepartially incorrect - of course it's possible to invent a human language, eg. Esperanto, Volapuk, Solresol, Ido, Intal, Glosa, Klingon, Neo, Babm, and hundreds of other invented languages.
Before Klingon (or "TLHINGAN" as it is known by the Klingons) was invented by Marc Okrand, the Klingons spoke many different languages and dialects, but the most common administrative language for official purposes was a sort-of hybrid of Welsh and Zulu, but with an extra complicated tonal, click and mutation system. The mutations would vary according to contact words and grammatical structures such as gender and case, but also according to the attitude, mood, rank, nationality, height and shoe-size of the speaker and of the listener, the day of the week and the weather.
English does not have its roots in Latin. Its roots are in the Balto-Slavo-Germanic branch of Proto-Indo-European and it developed through the Western Germanic branch together with its near relatives, German, Dutch and Frisian. It also has a lot in common with the Scandinavian languages.
The Italic languages, including Latin and the modern day Romance languages, including French, had a completely separate development in the Celto-Italic-Tocharian branch. Latin has, of course, influenced English, mainly in vocabulary and, to a lesser extent, grammar, but each originally developed completely independently of one another.
you are all wrong I am sure that the english language was invented by Ethel Bickerthwaite aged 68 from Wigan she made it up as a diversionary tatic to confound the police who had arrested her yet again for soliciting on the forecourt of McDonalds
That is possible, because I've heard that story before (although I think it may be an urban myth) but why would it work as a diversionary tactic from her situation?