I'd be will to wager that English is at,or near,the top of that list.
English is the most widely spoken second language in Europe and in the world by far - no other language even comes close. In spite of claims that Mandarin Chinese is the most common first language, it is probably actually English, given the population of the former British Empire. After Chinese and English, it’s Spanish. English is also the most common official or quasi-official language, the language of business and of science. Official claims notwithstanding, English is spoken fluently by well over a billion people, and understood to a significant degree by something on the order of 3-4 billion. It truly is the closest thing we have to a global language, thanks to the domination of the globe by first the Brits and then Americans for the past few centuries.
At any gathering of Europeans where native languages differ, the language of conversation is almost always English.
When I was a kid, English speaking Europeans and Israelis spoke with a pronounced British accent. Not any more. They speak with pronounced American accents. Interesting.