I wonder if "g" (glad) must turn into "zh" before "s" in Russian.
An adjective "peterburzhskyi" can be made of the noun "Peterburg"; something
similar may be observed in the pair of "drug" (friend) and "druzheskyi"
(friendly). But the cover of my old Russian LP of Bach's "Brandenburg
Concertos" says "Branderburgskye koncerty", no "zh" !

Juozas Rimas