“换言之”常见的英文表达有 in other words、that is to say 或 to put it another way。
In other words：最为常用，表达“换句话说；也就是说”的意思，用于进一步解释或重述之前的内容。
例句：He's not very sociable. In other words, he doesn't like to meet new people.（他不太合群。换句话说，他不喜欢结识新人。）
That is to say：同样表示“也就是说；即”，语气稍正式，用于对前文进行精确解释或补充说明。
例句：The project will be completed by June. That is to say, we have about three months to finish it.（这个项目将在六月前完成。也就是说，我们大约还有三个月的时间来完成它。）
To put it another way：意为“换句话说；从另一个角度来说”，用于从不同角度或方式对前文进行阐述。
例句：He's a bit stubborn. To put it another way, he doesn't like to change his mind easily.（他有点固执。换句话说，他不喜欢轻易改变自己的想法。）