If the answer to this question is yes that could redefine the Thracian input into the Bulgarian nation and language. Why am I even raising this question?
1. According to most linguistics there Thracian was very similar to Baltic, some classify it as south Baltic...
2. Baltic is very close to Slavic...
3. So that means that Thracian must have been quite close to Slavic...
4. Bessi (Thracian tribe) in 570 spoke their language:
In 570, Antonius Placentius said that in the valleys of Mount Sinai there was a monastery in which the monks spoke Greek, Latin, Syriac, Egyptian and Bessian.
The origin of the monasteries is explained in a mediaeval hagiography written by Simeon Metaphrastes, in Vita Sancti Theodosii Coenobiarchae in which he wrote that Saint Theodorius founded on the shore of the Dead Sea a monastery with four churches, in each being spoken a different language, among which Bessan was found. The place where the monasteries were founded was called "Cutila", which may be a Thracian name.
It has been argued that the name "Bessam" used in the Sinai region could be a corrupt version or alternate name for "Persian", "Slavic", "Iberian" or "Armenian", but there is nothing to indicate that.
Conclusion of the abovementioned facts: Thracians and Slavs spoke related language, close to each other (if Thracian was really close to Baltic). Thracians spoke the language when Slavs were entering the Bolkans. Could this mean that the Slavic in Bulgarian may also be Thracian?
Just a suggestion. I dont wanna start war. I just wanna provoke discussion. I dont say its true, just hipothesis.