"If the Celtic dialects are known to linguists and relate to other languages, then this suggests that these people preceded the Celts in Europe, and perhaps were driven back into the district they're in now by the invading Celts."
The Tocharian language A & B is an extinct European language that is most closely related to the ancient Celtic languages. The oldest paper ever found has Tocharian written on it and was found in China. Look to the east for answers.
It is suspected that the red-headed mummies found in the deserts of China spoke Tocharian.
Basque Y-Chromosome DNA is R1b, but somewhat different from Celtic R1b.
As one of my employees is fond of reminding me, Lithuanian has its roots in Sanscrit, and I think Latvian bears some similarities. At least, my Latvian employee and my Lithuanian employee can understand each other. It is a puzzlement how that language got from India to there!
Anyway, it's interesting to hear and think about. Check out www.chechnyafree.ru, and visit their music pages. May I suggest Aza and Marina Aidaeva.