Short answers, pulled from the story.
Aquitanian was the language of the ancient Aquitani, a people who lived in Roman times between the Pyrenees, the Garonne river, and the Atlantic Ocean. No surviving text exists in the language; all evidence comes from roughly 200 personal names and about 60 deity names preserved in Latin inscriptions from the 1st to 3rd centuries AD.
Scholars broadly agree that Aquitanian was a Paleo-European language genetically related to Basque. Linguist R. L. Trask argued it was a near-direct ancestor of Basque, while Lyle Campbell proposed it was a close relative rather than a direct ancestor. José Ignacio Hualde introduced the term 'Proto-Basque-Aquitanian' for the reconstructed common ancestor of both.
According to linguist Joaquín Gorrochategui, Aquitanian was spoken from Biscay in the west to the Aran Valley in the east, and from the Aquitanian Plain in the north down to the Ebro river in the south. Inscriptions have also been found as far south as Soria in Castile, suggesting the language covered a wide area.
The only evidence is onomastic: roughly 200 personal names and about 60 deity names recorded indirectly inside Latin inscriptions from the Roman imperial period, primarily between the 1st and 3rd centuries AD. No continuous Aquitanian text has ever been found.
Several Aquitanian onomastic elements can be matched to known Basque words: andere means 'woman' or 'lady', umme means 'child', sahar means 'old', gorri means 'red', bors corresponds to 'five', and atta means 'father'. These meanings are determined by comparison with modern Basque and the Proto-Basque forms reconstructed by linguist Koldo Mitxelena.
Yes. The Gascon language, spoken in the same region in later centuries, carries a substrate from Aquitanian, with certain words related to Basque. Aquitanian also came into contact with Gaulish near Toulouse and the Garonne river, and with Celtiberian further west, leaving traces in personal names and place names in both directions.