It seems that English is the language with the most words, with a total number of words estimated between 500 thousand and 1.2 million. But we can not be sure, because the statistics experts use take into account only a minority of languages.
Also, lexical counting is very difficult to do. An example is the German language, rich in compound words that are usually counted as a single term.
One of the explanations for English being the champion is in the number of countries that speak the language (45 nations with 330 million inhabitants) and the immense profusion of dialects.
It is impossible to know for sure how many words each language has. Dictionaries record unused words and fail to mention many new words.