Bulgarian is a Slavic language with close similarities to Russian.
By far the biggest obstacle to reading Bulgarian is the Cyrillic alphabet which was developed originally by the missionary brothers Cyril and Methodius. It has 30 letters and pronunciation is entirely phonetic.
In the bigger cities many street names and directions have Latin transliterations, and most restaurants have multi-lingual (BG/ GB/ RUS) menus  but it is still a good idea to familiarise yourself with the alphabet and if you are planning to stay longer to actually take some Bulgarian classes.