English does not have a single "standard" form. We can talk about American English, or British English, or Australian English, or even South African English. All of these varieties have some differences in vocabulary and pronunciation. Within any one country, there also tend to be different dialects. In the United States, people in the Northeast speak differently from people in the South. However, in general, speakers of English around the world can understand each other with little difficulty. Sometimes when people talk about non-standard English, they mean "slang" -- in French "argot."
Unlike Arabic, however, English is not diglossal. In other words, there is no uniform language equivalent to Modern Standard Arabic (اللغه العربية الفصحى ) as distinct from dialects such as darija. And while it might be difficult for a Jordanian to understand a Moroccan, an American is likely to be able to understand an Australian or a South African just fine.