“居间促成”可以翻译为“mediate and facilitate” 或者 “act as an intermediary to bring about” 。
“mediate”有“调解；斡旋；居中调停”之意，“facilitate”意为“促进；促使；使便利” ；“act as an intermediary”表示“充当中间人、居中调解”，“bring about”表示“促成；实现” ，整体表达出在双方或多方之间起到中间协调作用，最终促成某事的意思。
例如：
He mediated and facilitated the deal between the two companies.（他居间促成了这两家公司之间的交易。）
They acted as an intermediary to bring about the cooperation project.（他们居间促成了这个合作项目。）