I can understand him but I have to listen carefully because of his English accent. Words are kind of distorted.
I used to think the reason I had trouble understanding William was because of his English accent, but I've listened to other members of the RF speak and can understand them easily. I think it's just William. For someone who's presumably going to be making a lot of speeches later in life, he has a real problem with speaking way too fast and not enunciating his words.
Although, I've heard clips of other British people speaking and I can't say I understand them either! I guess it depends on the accent. But William (and possibly Harry) are the only royals I've had the problem with.