Answer:
If you are talking about a guy who is English or who speaks English, you would write it like so:
This English guy is on another level.
If you were talking about a guy named English, you would write it like so:
This guy, English, is on another level.
Also, if you were talking about the person's English in general, you would write it like so:
This guy's English is on another level.
Hope this helps!
