I’d have thought they would have kept English as it’s effectively a neutral language at that point - it would be convenient to avoid accusations of German or French dominance should either push for their’s in English’s place
One of the marvels of the EU institutional cathedral is the way they can manage effectively more than a dozen different languages. Yes, there are a handful of preferred ones, but in the end everything has to be translated to even the most obscure lingo. Sadly, instead of celebrating this epic taming of Babel, the French insist in narrow-minded cultural imperialism (as a reaction to Anglo-american imperialism, many of them would probably retort...), so they periodically pull these stunts. Nobody really cares, but if it keeps them invested in the Union, I'm happy to let them play king for 6 months.