As a writer I am authentic to my characters dialogue and world.

Being authentic to your characters do you write as they speak or do you write as you speak? If your characters are from a foreign country how would you know it if they spoke perfect English? I'm saying my characters are from Beirut and I'm writing their dialogue like they are English professors? Is that bringing the reader into their world? Does the reader believe they are living and from Beirut? My object as a writer is to take the reader first is to be original and second to take them into another universe and world and be believable.