“一人演几个角色的”可以翻译为 “a person who plays multiple roles” 或者更简洁地表达为 “a multi-role performer” （若侧重于描述具备这种能力的人） ，若描述某部作品里“一人演几个角色”这种情况，可以说 “a situation where one actor plays multiple roles”。
例句：
In this play, there's a situation where one actor plays multiple roles, which is quite challenging. （在这部戏里，有一人演几个角色这种情况，相当有挑战性。）
She is a multi-role performer, often taking on several different characters in a single production. （她是一名一人能演多个角色的演员，经常在一部作品中扮演几个不同的角色 。）