Getae and Dacians? Are they the same? Or is this unknowable?

[Rumo]

Well, Alan, there is a long debate between Walter Goffart and Herwig Wolfram about the ethnogenesis of Goths and other barbarian groups, and especially about the power of the oral traditions. Some of Goffart's arguments from The Narrators of Barbarian History were criticized by Wolfram in "Origo et religio. Ethnic Traditions and Literature in Early Medieval Texts", Early Medieval Europe 3 (1994) which prompted another reply from Goffart in "Does the Distant Past Impinge on the Invasion Age Germans", published in Andrew Gillett (ed.) On Barbarian Identity. Critical Approaches to Ethnicity in the Early Middle Ages (2002). Both latter studies were re-published in Thomas F. X. Noble (ed.), From Roman provinces to Medieval kingdoms (2006).

Instead of discussing every point Wolfram makes about Goths, Scythians, swords or gods, I'm bringing some excerpts from Goffart's article, which I believe will outline better the main idea:

• The fifty of somewhat more years we remember from personal experience embrace only recent times, current events. The distant past is quite different. It does not cling to an individual or a family; it is collective and deliberately taught or adopted. Possible distant pasts are multiple. The French of today can choose to descend from Lascaux cave people or Gallo-Celts or Franks or none of the above; the English can descend from Stonehenge builders or Celto-Britons or Saxons or Normans. These are learned choices.
  [...]
  Normally ignored, the distant past impinges on the present by deliberate choices, nourished by scholarship, erudition or religion. It does not exist 'out there', independently, as through an impassive river of memory flowed from a fountainhead downstream into the present. The Cambridge historian Eric Hobsbawm earned deserved praise for alerting us to the 'invention of tradition'. Invented tradition strolls hand-in-hand with the distant past, an intermediary between the opacity of remote centuries and the desire of the present to appropriate alluring days of yore.
  The distant past, of which no one has a direct memory, bears on what persons want their collectivity to be or to become. [...] When a recent article [my note: Goffart refers here to Wolfram's article mentioned in my introductory paragraph] labours at the anachronism of having medieval Scandinavia illuminate the Migration Age, we are put in mind of an 'invention of tradition', rather than normal history.
  [...]
  Wolfram contrasts himself to the 'positivists' - once a term of praise - who, he claims, are horrified by the biased historical writing of the 'compilers' of origines gentium; like him, everyone should accept that 'there exists an ethnic memory which can reach back over many generations. It includes genuine onomastic material and recounts theogony and ethnogenetic processes about which we would lack all other evidence'. Woflram takes it as a premise not needing proof that many generations of ethnic memory heartened the Germanic peoples.
  [...]
  Wolfram casts off the normal rules. Simple verification is the common ground among scholars. Wolfram's discourse is often beyond verification. 'In fact, there were continuous migrations of small warbands who were forced to go into exile. Groups of 200 or 300 warriors at the most left home due to internal strifes and feuds': the words are spoken confidently, with precise numbers of emigrants and the authenticating phrases 'in fact' and 'at the most'; but Wolfram knows as little as everyone else about warrior departures. 'One of Woden's many divine names was "Longbeard"': fair enough, but this is not general knowledge. Wolfram needs to share with us how he knows this. Certain names (such as 'Goth') 'mark their bearers as reborn divine ancestors'; Wolfram affirms this often, but without disclosing what makes it true. With only the word 'witches' in hand, he spins imaginary stories of tension among early Goths and expects them to be believed. The situation does not always improve when verification is possible, such as with the seventeen Alban and Gothic kings. Their alleged parallelism proves wrong when checked. Wolfram's argument needs a canonical number, familiar to educated men: it does not exist; the number of Alban kings varies from one author to the next. As for the 'genre' of origo gentis, of great importance to Wolfram's theme, it is a tissue of misunderstanding and distortion; the 'genre' evaporates when severely verified. There are histories of Goths and Lombards and many others; but there is no consecrated 'genre', ancient or medieval, of the kind fundamental to Wolfram's argument.

On a slightly different note, Goffart added in Barbarian Tides (p. 51):

• To hear Wolfram and others, Latin accounts of Goths, Franks, or Lombards should be regarded not as works of medieval historical literature, but as tribal histories faithfully safeguarding ethnic memories of religious intensity. Provided this channel is allowed to exist, large quantities of substantive "Germanic" content can be sent scuttling along it to the medieval world. To Wolfram, mere names and words divulge whole episodes of lost history in surprising and improbable detail. It has been ever so in the optimistic erudition of deutsche Altertumskunde, in which, to take a salient example, the island of Bornholm in the Baltic has only to bear this name in order to prove that the Burgundian people originating from there or at least pulled in for a little rest.

For variation, here're some excerpts from an overview article authored by Susan Reynolds, "Our Forefathers? Tribes, Peoples, and Nations in the Historiography of the Age of Migrations" published in After Rome's Fall. Narrators and Sources of Early Medieval History (ed. Alexander C. Murray, 1998):

• If mild scepticism about the old concept of the migration of peoples is in order, so it may be about two new ones. The ideas of a nucles or core of traditions (Traditionskern) and of ethnogenesis both seem to represent attempts to save something from old historiographic traditions that we have now formally discarded. [...] Some of the leaders of Goths or Burgundians may have been descended from long-distant ancestors somewhere around the Baltic. Maybe, but everyone has a lot of ancestors, and some of theirs may have have come from elsewhere. There is, asa Walter Goffart has repeatedly argued, little reason to believe that sixth-century or later references to what look like names for Scandinavia or for places in it, means that traditions from those particular ancestors had been handed on through thick and thin. We may guess at the kind of values barbarian leaders are likely to have had, and may suspect that they encouraged their followers to feel the kind of loyalty and solidarity that was often symbolized in myths of common descent and law. We also know from other societies that traditions can be invented, changed, lost, and borrowed by one group from another. That makes them, if anything, more rather than less, interesting historically. They tell us about the beliefs and ideas current at the time they were told.
  [...]
  Just as this may have not have been a period of exceptionally large and long migrations, it was not only period of ethnogenesis in Europe. Europeans seem to be rather good at creating new nations to suit their new states, whether in Europe or outside. Ethnic groups nowadays, moreover, are generally taken to be units of cultures and descent, rather than of government. The gentes, peoples, or nations that lasted in western Europe, although they believed in their common descent and culture, were in reality defined primarily by their political allegiance.

So here there are some reasons why I don't take Wolfram's theories at face value.
I know that speculation is unavoidable when weaving a persuasive narrative, but that doesn't mean we should speculate endlessly. A corollary of parsimony is that extraordinary claims require extraordinary evidence. When sweeping vast areas of space and long intervals of time, my opinion is that one needs better arguments than the few common (though sometimes only similar) names invoked by Wolfram.

Also some arguments you put forward seem to support rather a migration from Scythia to Scandinavia, not viceversa (e.g. Wolfram's "sword incarnation").

Many of these ritual swords were made by the Goths themselves, others by the Sarmatians, and still others by a Black Sea tribe known as the Chalybes. The finished blade was called "chalibis" by the Romans

It should be noted however that Chalybes lived somewhere on the south-eastern shores of Black Sea (Strabo, XI.14.5.), south of Caucasus. Herodotus (I.28) lists them among the Anatolian nations conquered by Croesus. The Latin chalybs is rather a borrowing of the Greek ?????.

By the way, I've never claimed that Gothic society spoke only Gothic. I said Gothic was the dominent language, the one spoken more or less "officially." Every army needs a uniform language and terminology, and Gothic was it.

It is my misunderstanding then. However at some point you supported the "axiom of the three generations": having a dominant language, the "joiners" (as you called them) will eventually shift to it (according to your own analogy, you "cannot speak a word of Gaelic or Italian, only English")

But I don't agree that any army needs an uniform language. Having bi(poly)lingual commanders is enough.