Adopting English as the main working language would save a lot of costs in EU from translations. Also one could have German, French and Spanish as side languages.
The smaller EU countries will have to accept English as main working language.
In many international business settings in Europe English is the norm. Why should
politics be different?
There are many reasons why using English makes sense, but saving costs on translation is just not that.
Unless you are bilingual the lost productivity of having to use non native language in business context would easily dwarf any cost savings, due to misunderstandings, miscommunication, not "Punkt genau" documentation etc ...
Heck, anyone can just try to do an IQ test in non-native language and see how the score drops.
Because politics is not business. Business is done with the criteria of efficiency, politics use the criteria of fairness. You should be able to speak to the EU institutions with whatever language you want. Not everybody speaks English.
Also, I don't know how many times you actually did business in an international context, and especially consumer facing stuff: you need to master the local language and good localization are often the key to success.
For example, the Spotify team did a great job customizing their product in different contexts, creating playlist that are clearly made by natives with the help and the insight of their data.
So it is absolutely not true that international business just happens in English: it might at a high level, but you need translations and cultural awareness to make it work.
In many international business settings in Europe English is the norm. Why should politics be different?