Parts of Eastern Serbia and Western Bulgaria speak a so-called Torlak dialect divided by the state border. The authors of the study aim to determine whether the state border that has existed in the microregion since 1833 is also a language border. There was no data on whether modern linguistic situations are situations of diglossia or diaglossia, and their extent; on the role of the so-called “horizontal” differences resulting from territorial variation and “vertical” differences influenced by the standard languages or regiolects; on whether individual dialects diverge, develop advergently with the standards, or preserve their basic state opposing it to the norm. The object of the study is two geographically adjacent local border idioms spoken in the Timok River valley and the western slopes of the North-West Stara Planina (Knjazevac, Serbia) and in the eastern slopes of the Stara Planina (Belogradcik, Bulgaria), respectively called Timok-Zaglavak in Serbia and Belogradcik, or Stara Planina in Bulgaria. The a