"Quisque est barbarus alio"

[Quercuum]

According to QuickLatin (which was probably used for this), ALIO is both Dative and Ablative. :)

But perhaps it's as you say, the popular vulgar form of Latin. Is there a source that states that ALIO is not both abl. and dat.?

When I check most Ablative and Datives, they very often share the suffix.

I've already specified that "alio" COULD be correct as a dative in vulgar Latin. I remember, but I'm not sure, that "alio" is also a form used in some medieval documents. Anyways, what I think is now important to do, is to choose which Latin we want to use in this game and, since it's about an era in which Romans spoke Classical Latin, I think that's the language we should use. We want to make this mod as realistic as possible, don't we? So "ALII" is the most senseful choice to take. That's all I wanted to say

P.S: I've also described how some adjectives aren't declined as other ones. In these adj. genitive and dative are completely different from the usual forms.
So you're right when you say that most ablatives and datives share the suffix, since it happens in the second declination, and the third for
what regards adjectives (Ex: "Lupo" is both dative and ablative for "Lupus", 2nd declination; "Dulci" is both dative and ablative for "Dulcis,-e", adjective
of the third declination), but there are some exceptions; "Alius" is one of these.

P.S. 2: Up to now, this is the only source stating what I said (Look at pages 258-259-260)
"http://books.google.it/books?id=_OJNfmxYi1IC&pg=PA261&lpg=PA261&dq=special+adjectives+latin&source=bl&ots=nLm-71l6Y-&sig=3iH2BkspzmJYF3pNVHTbFX_dCIk&hl=it&sa=X&oi=book_result&resnum=2&ct=result#PPA261,M1"