As far as the languages are concerned: absolutely no problem. Standard working language is English, you've got people from all over Europe working at the centre, and many of them only know their own language and English.
Dunno what to advise you about mentioning your failure for NATS testing... I'd simply put it in, but then again, I am an honest girl too.
Anybody experience with getting admitted to Eurocontrol after failing the NATS tests?