It was a change bought about by whining 737 captains complaining about having to speak english all day when flying with certain ex UK first officers, it is dated september 2006 and ratified by the VNV, perhaps you can find it on the VNV website in the archives.
The fact is that to join KLM now you must have been trained by KLS NLS or the Dutch military AND speak Dutch to Level B1 standard. These practices are illegal and protectionary.
KLM may be a great employer when on the inside, but their practices are far from fair. They took over Airuk within the D and K accord agreed that effectivly all the Airuk jobs over time would be transferred to Holland (KLCuk could not hire any more pilots). so in effect 250 UK jobs have been transferred to holland. Now apart from the ex UK guys can you give me an example of a NON Dutch National that has been employed by KLM in the last 5 years? Probably not, there are in fact a very few Belgian nationals who went through KLS but that is about it. So in reality 250 UK pilots have lost their jobs and 250 Dutch nationals have gained by this practice.
KLM is discriminatory through and through, this practice was bought about by the very right wing ex DFO E D H.