"Quisque est barbarus alio"

[Gaius Scribonius Curio]

According to the Lewis and Short dictionary the older version of the dative is found in Plautus (f. ~230 BCE). Furthermore, from the same source, the adverb alio is based on an old dative form, not the ablative you would expect, meaning 'elsewhere' or 'to another person or thing' similar to the Greek 'allose'.

Similarly, on 'quisque' the Lewis and Short states 'often used with reflexive se, suus'. On the other hand, often is not always, and it not necessary to do so.