As you are a French person who is trying to apply to a BA cadets scheme and also this easyJet scheme, I'd suggest not trying to be a know it all and letting the topic get back to what it is here for.
Well maybe not all, but having passed (successfully) those selections, I know what I'm speaking about... sorry ....
And yes you have to be fluent in german, but no it does not restrict it to german or swiss nationals.
Just take the example of SWISS, most of the cadets are not from Switzerland...
You can just work hard on your german and you'll be all ok.
Agree on one point: go back to EZY!