All the performance flights for badges and diplomas are in metric - meters of height gained, kilometers of distance flown.
Would you rather fly 50 km for your silver distance badge or 26.9978402 nm? They are the same (according to the Google calculator), but the former is less of a mouthful!
However we do use feet, knots and knots on the altimeter, asi and vario in the UK and the placard for my glider is marked in pounds and knots.