The crews I used to overnight with got 31000 yen a night.
Nope, they didn't. They may have received 31,000 yen but as others have pointed out, that was actually for two full days of allowances.
Qantas has some vagaries in its allowance system. Arrive at 0630 in NRT and if it's before 0730 in your departure port your first allowance is brekky. Depart after 1930 the next day and you get two full days of allowances. However, arriving in LHR at scheduled 0700 and if it was past 1300 SIN time, your first allowance was dinner. Arrive at 0500 and if it was before 1300 SIN time your first allowance was lunch. Swings and roundabouts. I've had 22 hour slips where I've received an allowance for 2 meals. I've had 10 hour slips where I've recieved the same. Its all a function of what meals were supplied on the aeroplane, departure time, flight time, etc.
Either way, as C441 alludes to, in most cases internationally the allowance paid is well below what public servants would receive for the same slip time. Domestically it's a bit more but we're taxed on that difference. I have no idea how our allowance rates compare with other airlines.