Few Main questions—Answered here.

Question: Is English prominent language in this universe, To the point even supernatural entities' are using english as a tool for communication between each other?

Answer: No, In simple terms—Verily No. There is universal translator which translates' the incomprehensible language of entities' beyond what human can conceive of. That incomprehensible language is translated into english for readers' to basically get a grasp on to whatever they are saying.

Question: So, In what manner does characters' comprehend each other as they communicate? For the most part, When human characters' meet some supernatural being?

Answer: It's quite simple—It's Universal translator. Human characters' probably have conversation through mouth but supernatural entity mostly respond in telepathic manner. However, Facial expression are what they are—As it only applies to means of communication and not facial expressions. So yea, Feel free to imagine some entities' just making facial expressions' and then staring at there adversaries'.