The dominant bee species in the country is what the local scientific community calls Apis mellifera carpatica. I say local scientific community, because to the best of my knowledge it's not an "officially" recognized (sub?)species. I think there is no centralized authority like a committee on species recognition, it works more like a consensus in the wider scientific community, that's why I put officially in quotes. The bee was described in detail and proposed as a species in its own right in the 1965 Apimondia Beekeeping Congress.
Apis mellifera carpatica is an Apis mellifera carnica (or the Carniola bee) adapted to the climate and conditions of the regions close to the Carpathian Mountains, hence carpatica in the name. I don't know if the differences described in the scientific paper are enough to warrant a new species, that's for entomologists to debate. I haven't looked into what those differences are (yet), and I don't think I have the eye for it now (maybe with some more years of experience and study).
While the A. m. carpatica (let's call it the Carpathian bee) is the most widespread in the country, some beekeepers imported and started breeding Buckfast as well. As a result, there are areas where the Carpathian bee is mixed with the Buckfast bee, and buying a "local" bee colony is not guaranteed to be 100% genetically "pure". A Ph.D. thesis from 2008 studied the genetics of 28 samples of 10 bees each from different areas in Transylvania, and found only 11 such samples to be pure Carpathian bees, 2 were known to be pure Buckfast (a priori), while the remaining 15 were a cross between Carpathian and Buckfast.
There may be others species present, but not in significant numbers, and mostly for research and experimentation.
 Foti N., Lungu M., Pelimon P., Barac I., Copaitici M., Mirza M. 1965, Researches on morphological characteristics and biological features of the population in Romania, XXth Jubiliar International Congress of Beekeeping - Apimondia, p 171-176.