"US xxx descend 4000 ft on QNH 1025"
"London information, could I have that in inches?"
"US xxx, apologies, descend four eight thousand inches, on QNH 1025".
There are some countries where different traffic uses different units. For example in France commercial air traffic uses feet, but some domestic GA uses metres, and I believe (2nd hand information) that in Sweden civil traffic uses feet and knots, whilst military uses metres and kph. In Romania I've been given surface wind in metres/second and had to do some rapid mental arithmetic to work it out in knots.
We do need standardisation - personally I'd go for feet, knots and millibars and bin the rest. But if we all went for metres, metres/second and hPa at-least we'd be speaking the same language. It's the plethora that is dangerous.
Or perhaps a worldwide alternate standard. You either use m, m/s, hPa, litres
OR ft, kn and "Hg, gal. All pilots learn both, and we might be able to cope.
Oh yes, and at-least get rid of those strange aberrations - US gallons, kph, statute miles and mph - they don't help. Okay, maybe in aviation imperial gallons are the aberration, but just one PLEASE.
But I do really, really, hate getting into a strange foreign aeroplane and trying to fly a visual circuit with an altimeter in metres
G