Manitas - good answer.

Declan - The idea that the names of whole peoples, tribes or clans are given not by themselves was dscussed in another thread before; I was not convinced. Since the Kelts changed their tribal areas a lot by emigration over the centuries, their name is preserved in different countries as Galicia in Spain, Galizien in the Austro-Hungarian Empire, Galata in Turkey (you know, Galatasaray, famous soccer club is from this region), and in Palestine Galilee, some say.
Contemplating the names of Celtic countries we have two forms: Gallia, now France, and across the Channel Wales with the Welsh (or Welch, with Raquel and the Fusiliers).
Here the closing t-sound was omissed sometimes B.C., the Kelts were referred to as Galli by the Romans.
Whence the W instead of the K? Maybe the original form was a labiovelar sound, an explosive formed as a g at the velum (back from palate) and a w with both lips at the same time, of which sound two different forms were preserved incompletely. But that is not my turn to decide, I'm an orientalist. There the question arised sometimes, too.

Nerd - I think your prof. is wrong; Quixote must be pronounced Kishote. In Old Spanish X was used for the sound sh. This usage is preserved in algebraic equations. In Spanish translations of Arabic mathematical texts the x stands for Arabic sh, an abbreviation for shay' = the thing, here: the unknown thing.

Bagpuss - So you can be glad there are only skot-Scots and no ssot-Scots (except the guys who can't distinguish between soccer and rugger).

A final remark to this phonetical discussion: As de Saussure has pointed out, languages must be also looked at from the viewpoint of time. A syntactical example: In Germany we see a change of certain adverbs of comparison going on in our times. What was utterly wrong some decades before is popular usage now, and will be right later on. The former correct form will be wrong, forms correct some centuries ago will be forgotten.
So let it be with the pronounciation of the C of which I have given some diachronical examples in my former post. The Irish pronouncing it Keltic have my sympathy since they follow the same use like us Germans. In both countries the Celts/Kelts have or had their stay. But I also will respect the usual traditions of pronounciation of speakers thinking and pronouncing otherwise.

Wilfried