Soldiers take vacation twice a year.
Soldiers take two vacations in a year.
注意:
vacation/vacations的用法
第一句 - 每年两次休假,所以vacation是单数.
第二句 - 一年内休两回假,所以vacation是复数.
Soldiers前面是否要加The,看情况,因为The soldiers似乎有特指的意思,但又不明确,甚至带有点贬义.或写成Our soldiers/The PLA soldiers比较顺口,Our soldiers有亲切感,我们的战士,我们的子弟兵啊.
在准一点,Our soldiers are allowed to take vacation twice a year.(准许之意）