[gumby]

Mandarin would open the EU to the largest number of speakers. Spanish would be a good second, if English is politically untenable, but of course it's already an official EU language so choosing it might annoy the other states.

Romansh is an European language not used in the EU; choosing it would level the playing field (and would not be so politically complex as another such like Basque).

[adventured]

> Mandarin would open the EU to the largest number of speakers

More people speak English than Mandarin and that language base represents a dramatically larger economy than Mandarin does.

The long-term trends favor English over Mandarin, not least of which is due to the difficulty of learning Mandarin vs English. The demographics underpinning Mandarin use are exceptionally bad in terms of direction, whereas the demographics underpinning English use globally are exceptionally good. The past 20 years has more than demonstrated the very low interest globally in Mandarin, despite the huge increase in China's importance and economy there has been no corresponding boom in the pick-up of Mandarin outside of China. In the next 20 years Mandarin will become a contracting language, while English will continue to expand globally. Over the time that China has been rapidly rising (since ~1990), English has only become more important globally, not less. Eventually, across this century, nearly as many people in China will speak English as Mandarin (they're very hard at work on achieving that; it'll be to their benefit and they full well know it).

[gumby]

> More people speak English than Mandarin and that language base represents a dramatically larger economy than Mandarin does.

Oh I agree but I was jocularly speculating on multiple constraints, to whit English is unacceptable as it would imply something favourable about those damned splittists; Spanish would not be acceptable because it would elevate one European country's language above others (though wasn't that the de facto story about English before Brexit?) etc etc.

In a different comment I argued for English because is not the selected language of any EU country.

Hmm, German might be a good choice as it is the EU language of three nations, so has a "majority vote" :-)

[dragonwriter]

> Mandarin would open the EU to the largest number of speakers.

No, making Mandarin the working language of the EU bureaucracy wouldn't open the EU up to any additional people, and the vast majority of Mandarin speakers are subject to one government or another that has no interest in the EU (and particularly, for instance, being accountable to the European Convention on Human Rights.)

> Romansh is an European language not used in the EU; choosing it would level the playing field

No, it wouldn’t. In terms of making communication within the levels of the bureaucracy to which it applies all but impossible, sure.

Not sure why that would be the goal, though.