The Germans and the Slavs are essentially the same folks, but their small leadership elite spoke a Western Indo-European language in the same group as Italian. Slavs to the East came under strong Greek influence, hence the development of distinctive Slavic dialects to the East.
The Celts were Celts, and spoke non-Germanic languages. The Greeks thought of them as barbarians in an earlier time, but the Romans thought of them as nearly hereditary enemies and very dangerous.
Now, to run this back a little bit further, Israel may have had millions of people, and maybe not, but they did not end up in Ireland, particularly when the Assyrians wanted to ship them out to Afghanistan!
Then there's a very long history of Jewish merchants traveling all over the Mediterranean basin, the Red Sea basin, and the Indian Ocean. They left their offspring and traditions behind. Modern DNA studies have found numerous groups that have males with the unique Y chromosome found only in the genotype of Aaron's descendants. The people who call themselves Palestinians cannot be differentiated, genetically, from the Jews in fact. Since most of those guys have grandparents and great grandparents who lived in different Arab and Turkish speaking parts of the Middle East, this raises a great question about whatever possessed these Moslems who are obvious descendants of the ancient Jews to return to the Promised Land in this modern time.
Do you think maybe God spoke to them in some way?
Notice that the Irish are NOT going to Israel or the West Bank!