Wouldn't the International Phonetic Alphabet be a good starting point ?
If you read English texts from the wrong side of the pond, there's some spelling divergence, and if you read old enough texts, there's more. And of course we have new words, and new uses of old words, such as literally which now means figuratively.
But if you read old books of rhymes, you can see that spoken English has diverged a lot more -- many clever rhymes of the past no longer sound rhyming.