So, if it's from the author's perspective, it's either RL Welsh in the Story, which makes no sense, or the author interprets the Story's language, whatever it is, into it's closest RL approximation, which happens to be Welsh.
Actual Welsh in the Story Universe makes little to no sense, IMO, since the creation of the Welsh language would have to be amazingly similar to how Welsh came about in RL.
TL;DR Either way, Welsh still doesn't need it's own Wikipedia Entry. Story-wise or RL-wise, everyone knows what Welsh is. :PÂ
....
All Hail Welsh.