So it's really good to know that we have two Celtic languages on DL now. One from the Gael branch and one from the Brythonic. My question is...
what do you guys think is the intelligibility between Irish and Welsh?
Also, anyone know if it's true that Welsh/Cornish/Breton speakers understand each other fairly well?
the answer to the first question is: about none. I was learning these two languages at the same time and it was hard for me to find any similarities beyond some grammar features. yes, they do similar things, but not always in the same way or the same places. vocabulary technically comes from the same sources, i.e. proto-Celtic plus quite a lot of Latin and Germanic influence, but again, words were processed in different ways and often bear little resemblance. phonology is completely different too. generally - no chance to understand one when only speaking the other.
Welsh, Cornish and Breton belong to the same sub-family of Celtic and thus are far more similar to each other, though a 'fairly good' understanding sounds a bit far-fetched to me. however, I have about zero experience with the latter two, so I'm no expert here.
Many words in Cornish are similar (if not the same) as Welsh. However, the structure of Cornish can be quite different from Welsh. I'm led to believe that Cornish structurally has more in common with Breton than it does with Welsh, but I'm not familiar with Breton so couldn't really say.