For the 10 past years, the trend has been more and more to accept the idea that the Celtic languages would have been present in Europe during the IInd millennium, during the late Bronze Age (V.Kruta, D.Vitali, B.Cunnlife,…).
Obviously it is a speculative idea, but it is the hypothesis I prefer.
Among these people, among them being Celtic speakers, some cultures would have emerged, as the Hallstatt, La Tene, Celtiberian, Armorican, British… cultures, related or not related one to another.
For instance, V.Kruta explains that some “latenian cultures” could have emerged independently of the “La Tene” core, as the effect of the Greek, Etruscan and more generally Mediterranean influences on different Celtic people could have had about the same results.