"他们真能干" 这个表达在英语中可以表达为 "they are really capable" 或 "they are really competent."
这个表达的意思是指这些人非常有能力，能够顺利完成任务或者做出贡献。
下面是一些例句：
"I was really impressed with the team's presentation. They are really capable."
"I have no doubt that Jane can handle this project. She is really competent."
"干" 这个词在中文中通常用来表示 "to work" 或者 "to do," 但在这个表达中，它的意思是 "to be capable of" 或 "to be competent at."