"成千上万" 在英语中读作 "thousands upon thousands" 或者 "thousands and thousands"。
这个短语是由两个独立的词组组合而成的。 "thousands" 是英语中表示 "成千" 的词，而 "upon thousands" 或 "and thousands" 则表示 "上万" 的意思。
例句：
There were thousands upon thousands of people at the concert. (音乐会上有成千上万的人。)
The company makes thousands and thousands of dollars in profit each year. (公司每年的利润是上万美元。)