Arguably there is no "English" language, but instead a hybrid of several other languages ... in future, I expect most languages to move in this direction - adopting and adapting words from other languages - hence less uniary pronunciation. Perhaps Finnish language will be an exception.
There are a number of English languages, official English of USA, of UK and so on.
The official rules however do not keep up with the current language and it's changing grammar rules and new words.
Through all times languages have changed due to necessity and to extensive contact with other languages. They're still their own languages while having a history - current English is clearly different from that of medieval English unless you know people who write "yong bacheler", who would then be speaking the old way.
So, for instance in US due to there being an actual group out there somewhere deciding what is correct grammar and there being institutions that try to enforce those rules there will be a unified formal 'correct' language which a lot of people will consider to be just that - the official correct form. All the alternatives are just dialects grouped around the main thing and you can use any dialect but when you need to 'get official' you write your best official language you know and can.
While so it is possible that US and UK official rules may further distance from each other as they have separate authorities on the language and separate institutions for enforcing it. If they had unified ones then their official languages would always be the same while having US and UK dialects.
Hybrid languages don't really work as such as two languages truly merging or it is very, very rare. Instead you'll have a number of languages that due to constant contact and ease have shared etymology and shared root words for things but the actual words are incorporated to their existing grammar rules and structure of the language. So for instance a country with object adjective structure can have the exact same words as another adjective object language but they're not going to change their word order. Sometimes some dialects converge in the tone and pronouncement but those will just be two dialects in different languages that are close.
So you can have an English dialect which is so close to French that a French person can make out most of what you're trying to say while some English person not used to that dialect will find it difficult to understand.
The languages just don't merge easily.
Mä refreshaan mun youtuben layoutin, uploadaa mulle se konfiguraatio sieltä pätchistä niin mä koodaan upgradet ineen ja online. This is 100% Finnish. The words here are fully integrated to the language. Just like if you were doing fencing and you used a bunch of French or Italian words, terminology that had been fully integrated to English language - it would feel like using English because it would be so, just like coup d'etat is English, often shortened as coup, an ordinary everyday term and you won't feel like you're speaking some hybrid language using terms like a la carte, amour, attache, banquette, brunette, bureau, cafe, concierge, etc.