I know this thread is pretty old, (like moi) and some of you may find this solution helpful or even amusing, but I've got the absolute perfect answer, for me anyway, to get read back instructions no matter what length, complexity, speed or accent of ATC controllers right first time without writing anything down on paper or worse, "say again".. It's something I put together myself which I call "Read Back Correct" and it really does the trick like magic. Here's how: £10 hand held Dictaphone from ebay with its mini mic placed in my headset ear piece. After my request to ATC for whatever, on release of PTT immediately press REC on above device. When he's done saying his stuff to you and himself actually, release REC and device auto rewinds in a second or two. Lean forward to device (secured next to my keyboard), so that my headset mic is near the device speaker, press device REP and my PTT together. At the end I chip in my callsign, release PTT. Result, after a moment of stunned surprise, the only possible reply from ATC: "Read back correct". Of course you may not have understood a word of what he said, but now you've got it on tape you can replay ad infinitum and even slow it down. Now that's magic!
Cheers, Dennis