Short answers, pulled from the story.
Thracian is generally agreed to have been an Indo-European language, though its precise linguistic affinities are poorly understood. Modern textbooks usually treat it as its own Indo-European branch or group it with Dacian to form a Daco-Thracian branch.
The Thracian language was spoken in ancient times across what is now Bulgaria, Romania, North Macedonia, Northern Greece, European Turkey, and parts of Bithynia in Northwestern Asiatic Turkey.
The exact point at which Thracian became extinct is disputed, but it is generally accepted that it was still in use in the 6th century AD. In 570, the traveler Antoninus of Piacenza recorded monks at a Sinai monastery speaking Bessian, a Thracian dialect.
Only four Thracian inscriptions of any real length have been found: the Ezerovo ring, the Kyolmen inscription, the Duvanlii ring, and a damaged stele from Samothrace. None of them has been translated to the satisfaction of the wider Indo-European scholarly community.
The Ezerovo inscription is a gold ring found in 1912 near Ezerovo in Bulgaria's Plovdiv Province, dated to the 5th century BC and inscribed in Greek script across 8 lines. The scholar Dimitar Dechev, Germanised as D. Detschew, proposed a translation after separating its run-together letters into words, but it has not achieved wide acceptance.
The classification of Thracian is disputed because so little of the language survives, leaving room for competing theories. The linguist Harvey Mayer proposed that Thracian and Dacian belonged to the Baltic branch of Indo-European, but that idea has not achieved general consensus among linguists.