A common critic we hear about an EU wide army is What language are they gonna speak but let’s forget Europe 2024,
Rome had a huge empire over the whole Europe, I may be wrong, but I don’t think that commoner spoke proper Latin in remote province. What happens when they join the legion ? Would the units be split by origin region (Dacian with Dacian, Lugdunumese with Lugdunemese) with only officer speaking latin ? Or would you merge legionaries from different province (So you have Tingitanian, a Lustitanian and a Thracian in the same unit) and give them a crash course in military latin (the way the french foreign legion does? ) Even going as far as Rome, Karl the great empire also spread over half of Europe, and modern European nation used to be way more multi-lingual than they are today, and most likely a random southerner/northerner in Britain, France or Germany couldn’t talk to each other.
So how did ancient armies managed the language question ?
Latin was the market language of Rome, and commanders/generals would have issued orders and received reports written in Latin.
Most soldiers would have spoken it, including the local auxiliaries that were conscripted. (Or at least a pidgin version of it.)
Even if the conscripts would speak whatever amongst themselves, they’d have understood Latin. (It’s also very likely that foreigners brought into the province would pickup at least a pidgin version of the local language.)
To clarify, this would be like the French foreign legion not speaking French. (The do. Maybe not natively, but French language skills are necessary for conscription.)
The issue at hand is that the EU is not an empire, it’s an economic alliance of sovereign countries each with whatever language they happen to speak. For an empire, it’s easy to dictate things like “Latin is the official language, all business is conducted in Latin.”