Daionii
'Wales' comes from an old anglo-saxon word 'walas' which means 'foreigners' (or something like that)..
Interestingly, this was mentioned in tis book i'm reading. the anglo-saxons and the britons had a war after the fall of the roman empire. the anglo-saxons seized all of what is now southern england and pushed the britons north. the anglo-saxons henceforth referred to the britons as "walas" which means, as you said, 'foreigners', or 'strangers'. thats why the area that the britons moved into became known as Wales =)
Rilian Sharp
I think it's probably the same way the people get the name. It probably originates from their word for "human".
this actually reminds of the word for the gypsy people. they call themselves--and its starting to become recognized internationally--"Romany" or, specific to the central european branch, "Roma". in their language, called Romani or more specifically, Romani ćhib, those words mean "people" or "human"