The higher the better... of course... )
Well, the 4th level includes understanding of different accents, so you should know that 'flaps' can be 'флэпс, флапс, эфэлэйпиэс, влабз' and so on )
But usually all you need is just some common sense and understanding of what they talk about in general, like to distinguish landing from takeoff, so it would be easier to understand the situation (and 4th level is about situations). Say, you won't ever say "FLAPS 40" after "TO/GA", never, so if you heard one of that you can immediately understand what's that shit all about).
But still you should know not only the names of all that stuff, but something about weather, wind, politics, borders... that's for general talking part, and you would need to make your performance passable enough here to get that 4.