In all fairness, I think it’s a good system to require German for a German company, French for a French company and Dutch got a Dutch company. It’s not discriminating, it’s culture.
if you apply for a “normal” job on the ground, they check if you fit within the company culture and atmosphere, and I believe airlines have the right to do the exact same.
At this moment in time it might not seem “fair” to others that language is the only thing in the way of getting a certain job, but I guess airlines aren’t waiting to assess 20k applications. It’s a divider which makes their work easier as well.