He would use terms like "bloody hard" or "wet blanket" which I would doubt are taught to foreigners learning English even with British spelling.
However - his spelling was a bit inconsistent. The "Len Sassaman" theory is interesting - as he was known to write in a somewhat British style (for whatever reason) - but not consistently - and was in the right timezone at the time. Or perhaps Satoshi was a synthesis of multiple different people which would explain a lot of the inconsistency as well.
Nigerians, for example, follow this standard and they have 4 times the population of the UK.