Nice find. The inscription reads 'This helmet was worn by an '88 January class'. It is written in Serbian ekavian dialect. To my understanding, Yugoslav army admitted new cadets twice a year--in September and January, which is why the term 'januarac' was used. It is essentially a made up word, an army jargon loosely translated as 'Januarian'.
The word 'guja' is a slang for snake. The inscription on the liner appears to be someone's name, maybe 'Beržaj Stjepan', which sounds like a Croatian name (last name first, as per local custom).
Hope this helps.