We used to take baby VC10K pilots to the US to expose them to a number of new situations - high temp / mil ops / busy civil ATC etc.- all achievable within a few days.
I found US RT 'different', but never impossible. Civil Center controllers were mostly fine, as were airport controllers, but many military ATIS readers were an idiotic liability.
Landing at Honolulu the crew was told "Next available, Ground point 9 when off". To me, sitting on the jump seat, that was blindingly obvious; take the next exit, then call Hono' Ground for taxying instructions on the VHF ground frequency which ends in .9. But no, the crew blundered off onto the next exit, then turned straight onto the taxiway without calling Ground, causing a 747 to come to rather a rapid halt, then struck up a conversation with the busy local controller...
Only issue I ever had could be summed up as "Speak fast, speak twice!". Rapid clearance delivered at a tobacco-auctioneer's pace, ending in "Readback" isn't helpful - crews will often ask for a repeat. But they should be ready to note it down, of course.
"xxxAir checking in at 360" I thought was a great idea - it let us know that he wasn't at our level. Equally "xxxAir passing 280 climbing 360". But when I did the same, my training captain said it wasn't necessary "Because ATC already know that!". Well, they might - but other aircraft won't and it all helps to build SA!
But
please - no 'rounders' scores on 123.45 on the ocean!