To be clear:I am not one of the involved KLM students, but I happen to know the case very well.....
KLM has hired only few pilots in the last few years and at the time dozens were on a waiting list (as is the matter with LFT Bremen students now) As Lufthansa was in desperate need of pilots a deal was made with the KLM flightacademy. An understandable step as KLM flighttraining is very much like Lufthansas own LFT training scheme in Bremen/Arizona.
Let it be clear that all students went trough the same selection procedure LFT students went through e.g. DLR etc and many failed to pass as well. Also the FQ was part of the selection. This was done in German, which answers your question on the language. Eventually just over 80 joined the Kranich airline. (a couple of them returned to KLM one year ago)
Their German may not have been fluent at the time, but I reckon it has improved and has become better than your English
AR