English version comes after Japanese.
大企業にお勤めの方だと夏冬ボーナス各2～3か月ずつみたいのが当たり前だと思いますが、日本だけの慣習のようで世界的には通用しません。アメリカの会社に多いのは100%業績次第でボーナスゼロも当たり前にあります。
It's probably one of the custom among Japanese companies to pay 2～3 month salary twice in a fiscal year, one in summer and the other in winter. One explanation is that this bonus system is originated more than 100 years ago when merchants gave servants some extra money in summer and winter.