Quite so. Unless one also spoke the language of the other .
For some real, complicated history of languages in medieval Scotland have a look at en.wikipedia.org/wiki/History_of ... s_language and the main articles it references (tmk no German version of these pages, sorry).
Btw, isn't the ArM4 Vindolanda at the Hadrian's Wall situated in Northumbria? In that case the people around it - on both sides of the wall - would speak the Northumbrian dialect of Old English. That's English (Northumbrian) in ArM5.
As I understand, Gaelic and English are both Indo-European languages, and that's about how closely related they are.
English is more closely related to Latin - and during that periode, both languages would likely have been contaminated by the Norse languages spoken by the vikings. :-/
Actually, English is a Germanic language, not a Romance language. However, it was heavily influenced by French and Latin over the years. But at the time we're looking at it hadn't been influenced by them for nearly so long.