[#3Fan]

If they aren't being absorbed, if they're not subjugated, if they're in a large group, they keep their language. See, for example, the Romany Languages.

Europe was subjugated by Rome for hundreds of years. Latin prevailed as result.

[VadeRetro]

Europe was subjugated by Rome for hundreds of years. Latin prevailed as result.

The Romans taught Europe Latin it may have been a conqueror's language in much of Europe but it was the native language of the Romans. Who taught the Hebrews Celtic? These people are missing from your story.