If you by ex-CAI then you are buying "in" Egypt and everything is paid for in Egyptian Pounds. Even the taxes/surcharges. It's just that the underlying price for various parts of the total fare are in different currencies which are each converted to Egyptian Pounds on the day you pay. So:

Base fare ex-CAI: priced in EGP
Taxes: priced in relevant local currency, so GBP for luxury tax for flight out of London Heathrow, HKD for airport tax for flight out of Hong Kong etc.
Fuel Surcharges: I wonder actually, probably the airline's "home" currency.

But when you pay you pay a singe fare in EGP (for ex-CAI) which is calculated by adding up all those components, based on the exchange rate on the day for non EGP priced items.


FWIW, it's same for buy ex-USA. You pay one fare in USD but the amount you to cover the airport taxes all around the world on your fare are all converted from their home currency to USD within it so for the same route the final USD price will vary from week to week as USD varies.