The limit of the country of registration is the legal limit for the crew as far as I know.
Certainly not the case in the UK. If you carry out what is defined as a flight function or flight activity in the Railways and Transport Safety Act 2003 within the UK then the Act, and the limits contained within it, apply to you regardless of where the aircraft is registered. Several foreign pilots flying foreign registered aircraft have been prosecuted under the Act in the UK.
It is true that the Act extends to flight functions and flight activities carried out in UK aircraft outside of the UK and it's quite possible that other states may also extend their legislation outside of their own borders but that doesn't absolve you from requirements where you are.