(the official one, also used by BG government)
This system does NOT use any diacritics, but it is not perfectly reversible: e.g. 'a' and 'ъ' are both transcribed as 'a'.
Romanization from Bulgarian (Cyrillic) to Latin and back.
Romanization (one form of transliteration) is the process of transcribing text that is in a non-latin based writing system into a roman system, based on 26 letters with or without diacritics (like â, č and ě). For romanization of cyrillic-based languages there are a lot of different systems. These are the ones used for Bulgarian.