Visigoths were a branch of the Goths, who in turn belonged to the East Germanic tribes that between 600 and 300 BC migrated from Scandinavia to the region between the Oder and Vistula rivers.
Some researchers believe that the Visigoths are the same people as the Thervingi, as the sixth century AD historian Jordanes says that their kings, from Alaric I to Alaric II, were heirs of the Thervingian judge Athanaric. But the issue has long been debated.
Herwig Wolfram claims that vesi would be the term the tribe used to designate itself, while thervingi was merely a geographical identifier. This would explain why the term thervingi ceased to be used when the Visigoths were displaced by the invasions of the Huns.
In any case we know that the Visigoths invaded the Italian peninsula, sacking Rome in 410 AD. Then they settled in the south of Gaul as foederati (federated) of the Roman Empire, and in 507 AD, after their defeat by the Franks, they definitively established themselves in Hispania (partially dominated since 415) where they would create the Visigothic kingdom of Toledo.
The Visigoths came into contact with the Roman Empire and its language around the 4th century, possibly before their invasion in 376 and their victory at the Battle of Adrianople in 378. The language they spoke, and which we know as Gothic, they called Gutisko razda and it was spoken by both the Visigoths and the Ostrogoths.
We know it because, unlike other Germanic languages such as Burgundian or Vandal, whose written texts have not survived, some fragments of Gothic have survived to the present day. The oldest of these texts is the translation of the Bible from Greek by the Gothic bishop Ulfilas in the 4th century, which is preserved in the Codex Argenteus or Silver Bible (6th century copy of the 4th century original), on display in the library of the University of Uppsala in Sweden.
Both the Silver Bible and other later documents, for example the Skeireins (a Gothic word meaning explanation) from the Codex Ambrosianus, were written in Gothic using an alphabet whose invention is attributed to Bishop Ulfilas himself, with 25 letters adapted from the Greek alphabet with additions of runes and Latin characters.
The Gothic language was only spoken by the Visigoths of the Iberian Peninsula after the disappearance of the Ostrogoths from the Italian Peninsula with the Byzantine conquest. The conversion of the Visigoths to Catholicism in 589 was one of the main factors in its progressive abandonment. However, it continued to be spoken until the 8th century, probably until the time of the Muslim invasion.
A dialect of Gothic continued to be spoken in the Crimean peninsula until the end of the eighteenth century. It is mentioned by the monk Walafrido Strabo, who wrote in the first half of the 9th century and was abbot at Reichenau monastery. And later a letter from the Flemish ambassador to the Ottoman Empire Ogier Ghiselin of Busbecq, dated 1562, includes a list of 80 words and a song in Crimean Gothic.
Gothic is considered the oldest Germanic language for which there is documentary evidence. It became extinct without leaving any derivative languages and, in the case of the Iberian Peninsula, after the Muslim conquest the Visigoths who remained were diluted among the mixture of peoples from the different kingdoms that emerged (also in Al-Andalus) and replaced their original language with the new Romance languages.
But just because Gothic is an extinct language doesn’t mean it’s gone forever. There is even a Gothic version of Wikipedia, and J.R.R. Tolkien published a Gothic poem entitled Bagme Bloma (The Flower of the Trees) in the 1936 volume Songs for the Philologists. More recently, in 2015, a Gothic translation of Alice in Wonderland entitled Balþos Gadedeis Aþalhaidais in Sildaleikalanda by David Carlton appeared.
Jaindre, qaþ Katta, biwagjands taihswon pauta seinana, bauiþ Hattareis: jah aljaþ, wagjands pauta anþara, bauiþ Martjuhasa. Gaweisos ƕaþar saei leikaiþ þus: bajoþs woþs (“In that direction”, the Cat said, waving its right paw around, “lives a Hatter: and in that direction,” waving the other paw, “lives a March Hare. Visit either you like: they’re both mad)
Anyone interested in learning Gothic has many resources available online, including the Grammar of the Gothic Language written by Joseph Wright in 1910. And even free lessons on Youtube.
But what did the Gothic sound like? Because Ulfilas used the same writing conventions as the Greek language of his time, and this is well documented, it has been possible to reconstruct to a large extent the Gothic pronunciation through comparative phonetics, and by looking at how non-Greek names are transcribed in the Silver Bible.
Gothic used a prosodic or orational accent, that is, it depended on the composition of the sentence, instead of the typical Indo-European tonal accent (applied to the syllable of a word). Thus, as a rule, the accent was fixed on the first syllable of simple words. In compound words it depended on whether the second word was a noun, in which case the first syllable of the first word was emphasised, or whether it was a verb, with the first syllable of the verb being stressed.
Sources: Linguistics Research Center (University of Texas) / Dr.Pfeffer’s Gótica / Gothic Bible in Ulfilan Gothic Script / Balþos Gadedeis Aþalhaidais in Sildaleikalanda (Alicia en el País de las Maravillas en gótico) / Wright’s Grammar of the Gothic Language (1910) / Wikipedia.