That is a point that honestly breaks my suspension of disbelief. The emergence of such a language is implausible to say the least. It would be a nice touch if Sindome was set 850 years into the future, but with a mere 85 years forward I‘d say it is impossible for "Euro" to form. People seem to underestimate just how deeply rooted the different languages are in Europe. Those are often focal points of national identity, with much strife surrounding it. There are institutions like the Académie française whose sole purpose since its inception 400 years ago is to preserve the French language. There is the Vatican who uses the same language since millenia, a language that is otherwise dead. Just to illustrate my point.
According to the timeline of Sindome, Europe stayed at its core very similiar as it is today, just having seen localized wars, political upheaval and economic crises. All things that have occurred many times over the centuries already. Yes, I understand that Sindome takes place in a technologically very advanced time, but that is a sociological question and not a technological one.
Let‘s take a look at the two possible origins of „Euro“ (since I couldn‘t find that in the records here – maybe I just overlooked it).
First scenario: It is an artificial, planned language that was introduced by all the governments to simplify communication. First of all, there is no body of governance that could do something like that – the EU crumbled pretty early and the local governments have no reason to topple their own languages. Because that would mean a massive overhaul of the administration which doubtlessly would lead to chaos, with immense costs that would never reasonably be recoverable by what you save on translators and interpreters. That would mean completely rebuilding the education sector, with the same chaos and costs. It would mean incurring the wrath of most of the populace. In short, it would be an immensly unpopular, immensely costly, and immensely inhibitive measure that would never take off.
Second scenario: It is a ghetto language that evolved on its own and spread among the people. The problem with that is that there is no body to regulate the language, to codify grammar, spelling, pronounciation, vocabulary. There would probably be over 30 separate slangs in the mega-sprawl around Paris alone, with half of them not mutually intelligible. Not to mention all the other countries which would have entirely different slangs based on their official language. Those things that have the power to shape language – newspapers, movies, books, etc. - would still be drafted in the established languages, with maybe some words or phrases of the slang entering the mainstream. Much like English is depicted in Cyberpunk.
The most likely scenario would not be a new language emerging, it would be already established, big languages pushing out the smaller ones over time (either naturally, or with the help of force) – like it has already happened in the past (e.g. in Ireland).
My suggestion: I guess from a mechanical point of view the goal was to summarize all the many different European languages, because implementing all of them would break the - according to older forum posts already underused - language system.
That is understandable, but – it is entirely themely to leave the smaller languages out of it, because those languages would likely have absolutely no bearing on Withmore. Yes, that new immigrant can be the master of Hungarian, a poet of his time, but he would have a hard time finding anyone else speaking it there. So there is no reason for the language to be codedly represented.
I suggest taking one European language other than English and Russian and let it replace Euro. The language that is likely having the most bearing on Withmore. Seeing how Saedor-Krupp is one of the oldest mega-corporations and seeing how New Prussia appears to be the major political power in the Europe of that time, I guess German would be the best candidate for that.
I suggest implementing French as well – yes, France is a shadow of its former self, but the past glory of the language is likely continuing to have an effect a mere 85 years into the future, even if it is just that corporate citizens learn it in an effort to impress each other. And one extra language is not going to make or break the system.
