How many words should I know before entering an international business conversation?

Before speaking in a foreign language, the first concern for many is: I do not know enough words. So, how many words should I know to feel confident during a conversation? If we start thinking about it, we have the same problem in our native language. We may feel inhibited by not being as eloquent as our car mechanic, tax lawyer or IT specialist. For German, the Duden dictionary company searched their text databases and found more than 17 million distinctive words. Most of them are rare words and/or technical words, of course. No native speaker knows all words in his or her native language. Conversations, even concrete ones, are really open-ended, unpredictable situations. We cannot know for sure in advance everything that will be asked or said. That is why, even in the age of AI, students are still afraid of exams, job applicants are anxious before a job interview and spouses worldwide have misunderstandings. Therefore, we will never know all the words than can be possibly s...