Archeology identifies various material cultures existing over certain geographical ranges throughout certain period. It does not recognise any culture as "Germanic" or "Celtic" in itself.

Consider that Chernyakhov culture which was spread over much of modern Ukraine in 2nd to 5th centuries, appears to be the home of Slavic, Germanic (Gothic), Iranic (Scytho-Sarmatian) and Dacian speakers. They all shared burial customs, made same kind of pottery, raised same kind of crops and built same kind of houses, and in that they were different from Germanic, Iranic, Slavic and Dacian speakers who lived elsewhere under the influence of other material culture.

Of course, we can only see as much as archeology shows us, we can't know if they shared religious traditions (though shared burial customs are indicative that they did at least partially), dress or music (although one could theorise on that).

The point is, there was no Slavic culture, Celtic culture and Germanic culture which can be compared. There are cultures which are independent of language, even though some cultures most certainly covered the area of a single spoken language (for instance in Scandinavia).