Several but mainly in the cockpit
First was a near miss climbing over Belgium where the captain made small heading changes when we were on a radar heading..blamed me but I had told him that we were radar heading until level then own nav.
Some of the Swiss Germans had a habit of cutting corners especially on the Italian airway heading north around the military area near bologna. Always pretended they didn't understand but I was never sure.
Italian controllers would go ballistic and give us avoiding action.
Had one in Chicago were the captain didn't understand enter, cleared immediate take off in American speak..heavy jet on short final....the jet on approach "burnt" the approach..captain never realised what he had caused.
Changed my use of English so that they had to answer in a form which didn't include a yes or no response.
Far greater problem than accepted mixing different nationalities.
Heard several wrong read backs not corrected by controllers working Montpellier approach whilst gliding.