It depends on what Europe wants to be. The language is in some ways connected to the culture. Would Europe get a more Mediterranean savoir vivre if everybody spoke Spanish or French? I think so.
An ambitious and interesting option for Europe could be Arabic as the lingua franca. If Europe commits, other countries like Iran or India could also be interested in joining. That could create a huge area with a single language as long as it doesn't splinter into dialects like the current Arabic.
The point of speaking Arabic would be to have the same language as North Africa and Arabia. And once Europe speaks Arabic, neighboring countries like Turkye, Iran or Pakistan and India could see the benefit in joining.
This doesn't mean that those countries become part of the EU. It would just create a huge zone with a single language which has its own advantages.