Danish Portal for Slavonic, Balkanand East European Studies
[en] The aim of the pages that follow is to introduce the Bulgarian language to students who already have some knowledge of Russian. School of Slavonic and East European Studies, University College London
Foreign Service Institute (1961)
A Concise Bulgarian Grammar: Designed for advanced-level language users and linguists to compare semantic categories across languages. By John Leafgren, University of Arizona.
Macedonian: By Victor Friedman, 2001