UK ATC is normally very professional. I think many units could do with some new microphones though!! Often I am flying with 2 other pilots and none of us can make out what the ATCO said. Loud enough but totally garbled.
Abroad, many ATCOs should learn some English. Their standard practice is to ignore a request if they cannot understand it, which happens quite often in some countries because many ATCOs have no grasp of conversational English - only the few standard phrases.