I was wondering how you would translate the word Tyrfing/Tyrfingr, the modern name for a legendary ancient norse sword first wielded and named by the King Svafrlami Sigrlamisson of Gardariki. King Svafrlami, earliest record of mention being in the Hervarar saga from 13th century Iceland, was an ancient Germanic King thought by genealogists to have lived from 430-475 AD ruling the kingdom of Gadariki. So the most accurate translation that Svafrlami himself used would be in Germanic Elder Futhark?
You might already know this, and are just presenting it this way for simplicity and for helping to identify what you're talking about, but it's probably a mistake to treat Hervarar saga as a faithful report about historical events. Its accuracy is probably comparable to Vǫlsunga saga. The history of the Burgundians is better known than the events that would go on to underlie Hervarar saga, and a comparison of that to Vǫlsunga saga makes it very clear that the saga is not a reliable witness. For one thing, Garðaríki was not a historical kingdom in the time described by Hervarar saga, and is probably supplied by the saga compilers because their then-current idea of it corresponded more or less well to the geographical location of the events under discussion.
Anyway, the actual answer here is unclear, because the etymology of Tyrfingr isn't known. The primary theories are that it's related to (or literally the same word as) the Tervingi, an East Germanic people whose context was similar to that of the setting of Hervarar saga; and that it's related to torf, 'turf,' referring to it needing to be retrieved from underground. If the former is true, then it is actually more etymologically accurate to write it "Tyrvingr" (which does occur; but by the time it was written down there was no longer any difference between "Tyrvingr" and "Tyrfingr" in the Icelandic of the time, so that doesn't tell us anything).
If the former, then we would want to reconstruct Tyrvingr to something like *Terwingaʀ (ᛏᛖᚱᚹᛁᛜᚨᛉ) in Elder Futhark-era Proto-Norse. This is a little bit problematic -- we'd be more likely to see that develop into Old Icelandic as **tjǫrvingr, but there's also no really compelling reason to assume that it would have been loaned directly into Proto-Norse, and then followed a normal path of development from there. It's entirely possible it could have been loaned into North Germanic from and East or West Germanic language, and it would hardly be possible to say how that would effect its eventual Old Icelandic attestations.
If it's built on the word torf 'turf,' that is much more straightforward: the hypothetical Proto-Norse would be *turbingaʀ (ᛏᚢᚱᛒᛁᛜᚨᛉ).
However, Svafrlami, if this corresponds to a real historical figure, would not have spoken a language written in Elder Futhark; he would have spoken Gothic, or something much like it. This is a bit outside my expertise, but I believe these would correspond to something like:
*terwingaz > *tairwiggs 𐍄𐌰𐌹𐍂𐍅𐌹𐌲𐌲𐍃
*turbingaz > *taurbiggs 𐍄𐌰𐌿𐍂𐌱𐌹𐌲𐌲𐍃
(Note that in Gothic, "gg" is like writing "ng," like in Greek).
Hope that helps. Tumblr crashed twice while I was typing this so if something seems disjointed it might be because of that, feel free to let me know.
