、。
Japan isn't a polygamous country, dear.
Literal
Japan [topic-は] polygamy-system [copula-ではない][explanatory-んですよ], dear.
一夫多妻制 'polygamy' — literally 'one-husband-many-wives system.' The sentence-final あなた 'dear' is how a wife addresses her husband — distinct from the neutral second-person あなた. んですよ is explanatory with emphasis, with a tone of gently correcting someone. Domestic humor.