Dacian language
It is evident than languages of Thracians and Dacians were relative and quite similar. That is why Dacian was long thought to be just a Thracian dialect, a tribal variety together with those of other Thracian tribes: Getians, Mesians etc. But nowadays, when additional data was found due to archaeological and onomastic resources, it is clear that Dacian had some significant differences from Thracian both in lexics and in phonetics (practically nothing is known about morphology for both tongues).

The book by a Bulgarian linguist Ivan Duridanov gives a good piece of information about Dacian placenames: towns, rivers, settlements. The majority of town names in the area inhabited by Dacian tribes carries the final element -dava (-deva, -daua, -daba), while Thracian names, lying to the south, mostly end in -para (-phara, -pera, -parón, etc.) ‘a village’, -bria ‘a town’ and -diza (-disza, -dizos) ‘a fortress'.

Phonetics reflects that Dacian was probably more progressive than Thracian. It did not preserve most of diphthongs, which existed in Proto-Indo-European and are observed the same in Thracian. The long [e] sound turned into [æ] and then into [a], which is absolutely strange for Thracian. As for consonants, Dacian preserved voiced and unvoiced stops (b, d, g, p, t, k) which became aspirated in Thracian.