Uh, pretty sure the sisters bios say they are from the Ottoman Empire (Present day Greece).
*pulls out SC2*
edit: Actually just "Athens, Ottoman Empire (Turkey)", so yeah, hardly Namco's fault there.
Now Ivy's dad being count from SC1-4? That is their fault.
Absolutely - we don't use the title "Count" in England. Our equivalent is "Earl" - but strangely, "Countess" is the correct title for the wife of an Earl! They did correct it as of V.
On the nationality discussion, I guess it depends on the character - for example, Spain, Japan and England existed in 1607 within similar parameters as they do in the modern era (albeit with larger international territories) - England is still a kingdom nowadays, albeit a united one, and Mits is definitely a "Japanese" character and Cervantes is "Spanish".
Some characters like Voldo come from regions that no longer exist - the Kingdom of Naples is now part of Italy as a whole, so we default to him being "Italian", even though that is strictly speaking incorrect, (I guess he'd be Neapolitan?) Similarly with Talim as Rep mentioned.
I think the character design is influenced more on a cultural basis (samurai = Japan, knight = German, monkey-shoutout = China), as opposed to a nationality box-tick. So someone like Setsuka clearly represents an element of Japanese culture - the geisha (or more accurately Oiran), but not necessarily by birth. Even someone like Ivy, who seems at first glance to be quite unstereotypically English, has clever cultural touches in her design, such as the Tudor Rose incorporated into her armor/earrings etc, which definitely shows that Namco do care about and research cultural relevance/iconography.
I really hope they do reveal more about ZWEI from his story - "Unknown" is (I assume) used to create mystery, but unless that mystery is revealed, I do agree that it is just lazy. Everybody comes from
somewhere, afterall. And if they are still going to produce detailed bios, they shouldn't skimp on the information - I personally appreciate the detail as it helps me engage with the character. Someone with "Unknown" on nearly all entries comes across as a flat character to me, but that's probably because I'm a bit of a culture&history nut :)