You often hear people say "you need to know x words in y language to be able to understand basic conversations.". This is a bit misleading, since the definition of "word" is varied. For example, in Chinese (yes, I know, Chinese as a language doesn't exist, but I digress) one character (one block) is one word. So this is easy. Then you have Japanese, where the same kanji (Hanzi, Chinese characters) can be pronounced differently, each with different meaning. You would assume Korean is the same way, right? That one "block" is one character. It is not the case, however. Korean is agglutinative language, which means you can stack suffixes just like Finnish and Turkish to morph a word.
Then you have English, which is quite clear how a word can be counted because it has space. What about languages that write words together without space? One could argue that Thai is like Chinese, that it has no conjugations and you can append a bunch of words together to form a sentence. The difference is in Thai, you would have to mentally break up each word. For example, the "word" "ตากลม" can be separated two ways: "ตาก-ลม" and "ตา-กลม," again, with different meaning.
And in Semitic languages, words are based on tri-root system, where you put consonants into a vowel pattern to conjugate. Speaking of conjugations, run, running and runner are from the same root, but would you consider them different words?
As you can see, how a word is defined is different. Some may argue different conjugations is enough to make it a new word. So if you know basic conjugations, say, five of them, and you know five root words. Now you know 25 words. Yay! Right?