I agree that the terms "language" and "dialect" should be better defined (although controversy would exist in any case). The "languages" used in the game are sometimes more similar to language groups, and sometimes they are actual languages. For example, we have "Scandinavian" and "Baltic" languages, but Cisalpine is different from Italian, and Portuguese is different from Spanish (instead of one Iberian language). I think the developers previously mentioned that they didn't want to weaken some dialects by splitting them into full languages. However, since the size of languages already differs greatly, maintaining historical accuracy should be preferable, if it's possible to do so.
As for the difference between a language and a dialect, it is often controversial, but with the inclusion of court and market languages, it can come down to these criteria (which of course could be expanded or revised):
1) Whether the language was or could have been used in government, as the language of administration, laws, or legal documents (e.g., court language).
2) Whether the language was used in commerce, trade, and craftsmanship (e.g., market language).
3) Whether the language was standardized (whatever that means) and has grammars, dictionaries, other linguistic works, and high literature.
It’s hard to find a sphere of life where Ruthenian wasn’t used in the EU5 timeline (except for liturgy). Furthermore, the West Slavic language was recently split into Lechitic and Czechoslovak, so East Slavic should be split too if we want to be consistent.
As I have outlined, with those criteria every dialect will be split.
Low German was a market language
Swedish was used for lawmaking iirc
Middle Dutch has an entire article on Wikipedia of everything that was written on it
Venetian was a Lingua Franca in the sea.
I do think Iberian split to Spanish and Portuguese is a developer bias, and they should be merged. Italian feedback thread is arguing for uniting Cisalpine and Italian. And weakening is not only about the area.
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