"Filister", which would not be understandable for many people, "prostak", which would be a very understandable insult, definitely a lot broader in meaning (an uncultured, undeducated, rude, vulgar person).
I have no idea if 'filister' has (had? does someone still use that?) a feminine version, but prostak will turn into prostaczka. Anyway, even if wiktionary gives it as one of the translations of a philistine, it's really a lot stronger.