Old English was probably still close enough to Gothic at that time as to be somewhat mutually intelligible - at most a gap similar to Dutch and German today. They may have integrated into local society more easily than it seems they would at first glance.
(This is speculative. There's nothing particular to support this other than coincidence in timing and geography.)
and in terms of communication, there is that Danish linguist who has a pretty good argument in favor of middle and modern English being more heavily influenced by Danish grammar than Anglo Saxon. Although these were Anglo Saxons, the influence/familiarity with Danish might have been well established
https://www.youtube.com/watch?v=9ZV1BOcGiV0
(audio) https://www.youtube.com/watch?v=wBio7c95QQE
https://partner.sciencenorway.no/forskningno-history-languag...
If HN is looking for a nice, non-technical, read this is a rewarding place to do it.
edit - her book is very readable, recommend
Dr Green has been doing ok on HN for several years.
But you wonder if there might have been interaction between the local Goths and the incoming Anglo-Saxon speakers, who surely would have recognized each other as distant linguistic relatives...
What other evidence would you expect to show what language the inhabitants spoke? Religious text (ie, almost all writing) would have been in Latin or Greek. Coins were shared across regions.
https://en.wikipedia.org/wiki/Crimean_Goths
"In the report made by Ogier Ghiselin de Busbecq in 1595 on the Crimean Goths, he claims to not be able to determine whether the Germanic peoples of Crimea were Goths or Saxons;"
and that - 10th century Vikings - all the way to the Black Sea:
https://en.wikipedia.org/wiki/Viking_expansion#/media/File:V...
So discerning the specific, even that large, Saxons or Vikings arrival and settlement from all the others Saxon/Goth and Viking presence there may be not much possible.
And politically today - on the orders of the Russian state the Russian historic science these days futilely tries to find evidence of pre-Viking statehood in the Rus as the real history of Rus state being founded by Vikings doesn't work well for the Russian nationalism, and having more Vikings (or Saxons) in the picture doesn't help that official goal, especially on the lands that Russian propaganda these days claims as "historically Russian" and with that claim being used as the pretext for the war that Russia is currently waging for those lands.
In the opposite direction (i.e. from South to North) there's this famous travel of Ahmad ibn Fadlan who wrote about the Vikings living on the Southern part of the Volga.
> His account is most notable for providing a detailed description of the Volga Vikings, including eyewitness accounts of life as part of a trade caravan and witnessing a ship burial.
I've read the French translation of his work (Voyage chez les Bulgares de la Volga [2]) and I have to say that it is quite interesting.
[1] https://en.wikipedia.org/wiki/Ahmad_ibn_Fadlan
[2] https://fr.wikipedia.org/wiki/Voyage_chez_les_Bulgares_de_la...
the map i linked to isn't "travel", it is "settlements". They settled as far as Black Sea and traveled even farther, like the South Volga you mentioned and even raided Iran shores of the Caspian Sea.
There were not much people to start with (and 500 ships in a raid is a like 5000-10000+ warriors which is larger then many cities at the time), and you're mixing 2 types of populations - all those people were nomadic dry land people while Vikings were settling along their trading and raiding routes along rivers and sea shores. The Azov Sea and the Don river were on their route into Caspian Sea. Vikings even tried, yet failed, to settle further into Caucasus :
https://en.wikipedia.org/wiki/Caspian_expeditions_of_the_Rus...
"The Rus' launched the first large-scale raid in 913. A fleet of 500 ships reached the southern shores of the Caspian Sea through the country of the Khazars. .... They sailed down the Dnieper River into the Black Sea, then into the Sea of Azov, then up the Don River past the Khazar city of Sarkel, and then by a portage reached the Volga, which led them into the Caspian Sea.[8]"
"During the 943 expedition, the Rus' rowed up the Kura River, deep into the Caucasus, defeated the forces of Marzuban bin Muhammad,[11] and captured Bardha'a, the capital of Arran. The Rus' allowed the local people to retain their religion in exchange for recognition of their overlordship; it is possible that the Rus' intended to settle permanently there.[12] According to ibn Miskawaih, the local people broke the peace by stone-throwing and other abuse directed against the Rus', who then demanded that the inhabitants evacuate the city. This ultimatum was rejected, and the Rus' began killing people and holding many for ransom. The slaughter was briefly interrupted for negotiations, which soon broke down.[13] The Rus' stayed in Bardha'a for several months,[14] using it as a base for plundering the adjacent areas, and amassing substantial spoils.[15]"