Bulgarian is written in Cyrillic, and even one or two words go a long way in Pavel Banya where the population is small and most daily interactions happen in Bulgarian. Locals are generally warm and patient with visitors who try, so polite greetings and a simple 'blagodarya' earn goodwill at the mineral baths, family-run guesthouses, and the local bakery.
Phrases are most useful at the spa reception, the kafana (tavern), the bus stop to Kazanlak or Stara Zagora, and the small market stalls selling rose products and rakia. Keep a note that older residents often understand Russian, while younger spa and hotel staff are more likely to switch to basic English—still, having Bulgarian ready is the smoothest route.