Question of the ethnic quality of Lusacian Culture :
I lack recent works about it but it seems the old scientists had ?ad hoc? theories, placing Lusacians of the shifting between Bronze and Iron ages among proto-Germans, proto-Slavs, Thracians, Carps (Carpo-Daces), Illyrians? broad choice !
It ?s hard to descriminate ethnies among cultures : ethnies change culture, cultures changes ethny?
To me it seems the Lusacian culture rather than the prototype of the Urnfields aspects is one aspect of the Urnfields, Urnfields born around Hungary/Austria, mixing diverse streams of culture, but with incineration which seems a recurrent trait of Late Neolithic cultures under southeastern influences. But I don?t believe in important cultures changes without some demic imput ; and more than one scholar mentions an encrease in demography : the problem is how to weight this demic input. Center Europe has been a crossroad of so numerous tribes in past ! (and to date too). But it?s not to say there has been always a complete melting of these tribes at the basic social level (even swords, tradable, showed typical geographical distribution for some time, and even when they were found almost all of them in Hungary, a central point).
Linguistically, I have pain to forget completely some phenomenons, even if some proximities can be discarded by peer examenation : the supposed devoicing and hard spiration of consonants in Rhaetian, Etruscan, Germanic, modern Hungarian compared to Finno-Ugric roots (in this late case I don?t know if these phenomenos did not occur before reaching Europe, I avow). What is maybe of some weight is some proximity in Venetic of basic words (pronouns) with Germanic and some phonologic similarities with Rhaetian. So I?m tempted to think that some linguistic phenomenons took their origin in Central Europe, for the most around Hungary, a crossroad, around the very Late Bronze/Early Iron and Hallstatt and I would discard coincidences. Spite the new mutations in High Germanic dialects compared to Low Germanic and ancient Germanic are similar but not identical, I still wonder if they would not be linked to an ancient pop of Tyrol surroundings, linked to something Etruscan-like.
So, maybe a population or Hungary or surroundings could be at the origin of the spread of a religion implying cremation, but it seems it had the support of some trade or partial colonisation, based on aspects considered then as a (material) progress ; the demography in more than a place confirms it. It is not sure this newcoming pop imposed everywhere its language, IE or not. The change has been either brutal and complete or progressive or incomplete (sometime crossed : old artefacts new burying, new artefacts, old burying ; look at Baviera : first cremations only for wives : exchanges ?), according to regions ; this last aspect discards the solution of an uniquely religious phenomenon, IMO. In Lusace territory, I think a new ethny took foot by South in S-W but it could not be a Slavic one, nor I think it was Celtic spite I believe Celts or some kind of Italics could have been the tumuli first intruders fromS-W Czechia, before Urnfields. After first change in Lusacian world (urnfields), I think the mode extended unevenly to other regions of Poland or Germany to other ethnies (and in other Europe regions the same mode). In Poland I think that in East we could have found some (proto-)satem langage from previous CWC, on the way to maybe Baltic-Slavic, not Slavic yet, whatever the tribes names. In West, I guess some proto-Germanics, and pan-Italics (Germanics show more grammatical ties with Balto-Slavic, and more deep ties too with Italics than with Celts, according to someones). Only bets before writings, if ever someones came to light.
