No idea if this works or not - just looked it up. Apparently for Sims 3 you could type in the cheat code “Englishspeakingsim” without the quotation marks. The cheat code is one word with no spaces. Press the “Enter” key on your keyboard. Now your Sims will be speaking English.
You may also find this useful - simlish to english translations (scroll to bottom for list of words and what they mean in english)
You must be registered to see the links
However after my search, not finding anything in which you can either change simlish to english (or any other language).