Back in ‘55 when we thought we were hot because we knew 20,000 words we were informed that English has two million words.
When I was in grad school (English) in the 70s, we learned in a linguistics course that best estimates placed English as having 600,000 to a million words. I did have a lexicography course -- word count in a language isn't all that straightforward, e.g., do you count "nonce words," those that show up for a year or two and disappear? do you count localisms? when does a word with two or more different strands of meaning count as two or more words? when does a foreign word begin to count as a native word?