Culture is a factor and a big on at that but,
It is by no means not manageable.
like Mathfox already said;
The big cultural difference (with a great impact on CRM) is that the Dutch (especially in the area around Amsterdam) are quite anti-authoritarian. A manager who just orders his subordinates around will be asked to motivate his decisions pretty soon. On the other hand, people on the work floor are not shy to warn when something threatens to go wrong. As preventive action managers schedule "meetings" where people can spout their issues so the manager can deal with them before they become problems.
The French culture is more one of respect for authority and good relations with the people around you. Potentially angering a colleague by saying he did something wrong is bad for the relationship. Don't dare to offend your chef! So problems often tend to simmer, unless someone finds out, leading to a French-style vocal explosion.
Is maybe correct now but hasn't always been the case.
Everybody here surely remembers and studied the effects of bad crew communications which was a great contributor to the Tenerife KLM-PanAm disaster in '77.
Also inability to speak English is more indicative of bad selection and subsequently bad training than purely culturally determined.
Eg.
I wouldn't exactly call the Japanese population proficient in the use of English but their Pilots sure seem to do things better than most of the other far east carriers.
Also they have adapted a more western style of working when it comes to cockpit procedures and the weight of the co-pilot in the decision loop, which isn't exactly a small feat given the importance of seniority in the rest of their working culture.